When philosophers at large are surveyed, we observe this distribution (N=1758 [source]. 59.16% accept or lean towards compatibalism; 18.83% accept or lean towards libertarianism; 11.21% accept or lean towards no free will):
But when we filter by area of specialization to be philosophy of religion, we observe this distribution instead (N=141 [source]. 30.50% accept or lean towards compatibalism; 53.90% accept or lean towards libertarianism; 6.38% accept or lean towards no free will):
Why?
My initial hypothesis was that there's a theism bias.
An earlier question noted that philosophy of religion has a theist majority.
If we look at your one link, we can see that's indeed the case:
| r: 0.45 | God: theism | |
|---|---|---|
| Free will: libertarianism | Accept | Reject |
| Accept | 167 | 134 |
| Reject | 147 | 1083 |
A mere 11% of atheists accept libertarianism, whereas 53% of theists accept libertarianism.
This may not fully account for the difference (it would seem pretty close to 54%, but 20% of philosophers of religion are atheists, which drags the number down). But it seems fair to say that this has the biggest effect, and the remaining difference may be more subject to noise.
Well, theists commonly accept that there's something "outside the physical"* (whatever that means), that there's at least one consciousness (a god or gods) not subject to "physical" (typically deterministic, or random) forces.
* There's a strong correlation between theism and rejecting physicalism - 94% of theists reject physicalism (806/(53 + 806)).
It's also a fairly common theist belief that human consciousness persists after death.
So it's not much of a stretch for them to think human action is not subject to deterministic forces, i.e. libertarianism.
As for why 47% of theists (and 89% of atheists) reject libertarianism, one might suspect that they see too much evidence that makes them think our actions are subject to deterministic forces, in the form of neuroscience, psychology and evolution, or they find libertarianism to be incoherent. For theists, this may overwhelm their theism bias, whereas atheists don't have theism pushing in the other direction. But this is much more speculative and based on my own views on the matter. It might also be that non-libertarian theists reject libertarianism exactly because of their god belief, i.e. God determines every event (as per user80226's link).
Educated guess: because most philosophers of religion are theists (see Why do most philosophers of religion believe in God?), and the Free Will Theodicy is widely used by theists in response to the problem of evil, which arguably only makes sense under an indeterminist (libertarian) conception of free will:
With respect to the question of the justification of pain, cruelty, and other evils in relation to God, it is important to acknowledge the significant role played in theistic thought by appeal to the power of human free choice. We have seen above that many of the theodicies on offer rely on it. One prominent way to defend the goodness and other perfections of God in response to the evils of the world is to point out that, after all, God did not bring about the Rwandan genocide or the Holocaust or someone’s sexual assault. Instead, these were caused by human actions, which the theist may suggest were freely chosen by perpetrators. On the free will theodicy, God remains an absolutely perfect being even in light of the suffering in the world, because it is created beings who freely choose to harm each other (and non-human animals and the environment), and none of this is God’s direct doing. What goes wrong in our world is not the fault of God but rather the fault of the wrongdoers who use their power of free will to act badly. The free will theodicist holds that it is a great good that God gave us free will and allows us direct the course of our lives by way our own free choices (Swinburne 1998). The result of the gift of free will to the billions of people on the planet is a whole lot of bad consequences from evil choices, which God is justified in allowing because of the greater good of the gift of free will.
[...]
Another difficulty facing the free will theodicy is this: whereas some philosophers think that free will would be ruled out by the truth of causal determinism (the hypothesis that at each moment there is exactly one future, given the laws of nature and the events of the past), other free will theorists believe that we can act freely even if causal determinism is true. Arguably it is crucial that the free will appealed to by a free will theodicist must be indeterminist (libertarian) in nature. (For exploration of indeterminist accounts of free will, see Clarke 2003; Ekstrom 2000, 2019; Franklin 2018; Kane 1996; Mele 2006; O’Connor 2000.) The free will theodicist thus must maintain that all compatibilist accounts of the nature of free agency, including those provided by Frankfurt (1971), Watson (1975), Fischer (2012), Nelkin (2011), and Wolf (1990), among others, are implausible accounts. In citing the free will of created beings as the greater good that justifies God in permitting instances of evil or the facts about evil, the free will theodicist also needs to hold that causal determinism is, in fact, false and that we human beings do have libertarian free will. Without maintaining these positions, the free will theodicist lacks an explanation for the violence and cruelty in the world that shields God and preserves God’s goodness, since God could have established the initial conditions of the universe and decreed that deterministic natural laws govern all events, so that the events in the world unfolded to include none that are painful, harmful or wrong. God could have done this even in worlds in which he created free (in a compatibilist sense) rational beings.
If you don't believe in God, and instead accept or lean towards an alternative metaphysical view, such as physicalism, then there isn't really an issue involved in discarding libertarianism in favor of alternative conceptions of human volition.
Because we can only be morally responsible for our deeds if we can exercise free will.
No free will means no sin.
Clearly, most theists would find that objectionable.
Mathematically, what we should expect is randomness, not complex order. The fact there is complex order can lead one to believe in a supreme intelligence organizing the cosmos. However, if the supreme intelligence itself operates according to pure mathematics, i.e. determinism, then we arrive back at the original problem, which is the supreme intelligence should itself just generate randomness, not complex order. The only way out of this mess is to posit some causal power beyond determinism, i.e. libertarian free will. In which case, belief in theism entails belief in libertarian free will.
