What is a “reason”? Nothing but a cause (that is meaningfully, reasonably, and predictably tied to the effect, perhaps). The only cases in which a mind has a spontaneous thought (that is, one with no reason for them), are “brain static” and Boltzmann brains. So your question is essentially reducible to the question of “Why am I not a Boltzmann brain?”
Edit: I’m not really sure that “reason” is equivalent to “cause”, on further reflection. There needs to be a deeper connection between A and B, if A is said to be the reason and not just the cause for B. So if the cause for “thinking that one has free will” is simply “that is how brain architecture works”, and not some previously-unknown phenomenon, that might not be seen as a reason for the illusion of free will.
What is a “reason”? Nothing but a cause (that is meaningfully, reasonably, and predictably tied to the effect, perhaps). The only cases in which a mind has a spontaneous thought (that is, one with no reason for them), are “brain static” and Boltzmann brains. So your question is essentially reducible to the question of “Why am I not a Boltzmann brain?”
Edit: I’m not really sure that “reason” is equivalent to “cause”, on further reflection. There needs to be a deeper connection between A and B, if A is said to be the reason and not just the cause for B. So if the cause for “thinking that one has free will” is simply “that is how brain architecture works”, and not some previously-unknown phenomenon, that might not be seen as a reason for the illusion of free will.