The probability has something to do with the number of people who believe it because it is possible that some of those people have a good reason to believe it, which automatically gives it some probability (even if very small.) But for positions that no one believes, this probability is lacking.

This can't be right. The number of people who follow any one religion is affected by how people were raised, by cultural and historical trends, by birth rates, and by the geographic and social isolation of the people involved. None of these things have anything to do with truth. Currently Christianity has twice as many people as any other religion because of historical and political facts; you think this makes it more likely than Islam to be true?

Suppose that in 50 years, because of predicted demographic trends, there are twice as many Muslims as Christians. You then seem to be in the strange position of thinking (a) Christianity is more likely to be true now, but (b) because of changing demographics, you will be likely to think Islam is more likely to be true in 50 years.

We do have information on what kind of God would exist if one existed: it would probably be one of the ones that are claimed to exist.

How do people's claims give you that information? Religions are human cultural inventions. At most one could be true, which means the others have to be made up anyway. If a God did exist, why is it more likely that one of them is true than that they were all made up and humanity never came close to guessing the nature of the God that did exist?

Anyway, as Nick Bostrom points out, even without this kind of evidence, the probabilities still will not balance EXACTLY, since you will have some evidence even from your intuitions and so on.

My intuition tells me that if a God of some sort does exist, the probabilities end up favoring a God that rewards looking at the evidence and believing only what you have reason to be true, but that may just be my bias showing.

Intuition about what religion is true is likely to reflect your upbringing and your culture more than the actual truth. Given that there's currently no evidence of any kind of God or afterlife, I can't see how there is any evidence that God X is more likely to exist than God Y.

It may be true that some people couldn't make themselves believe in God, but only in belief, but that would be a problem with them, not with the argument.

It's also worth noticing that Pascal's Wager uses a spherical cow version of religion. Some religious traditions might require actual belief for infinite utility, others just belief in belief, others just certain behavior or words independent of belief.