Why does evolution allow a trait which feels that we have free will?
The point of consciousness is to keep us with the illusion of "self", so we can function 'normally' with everyday acts of survival. For example, self preservation would be a difficult thing without consciousness for animals like us. More primitive lifeforms like bacteria reacts according to what's written into the genetic code in terms of their self preservation. I am thinking, animals like humans and similar animals with sophisticated central nervous system would need a very strong illusion, hence the consciousness.
Freewill is a complex subject I would imagine. In biological sense, freewill looks like a sure illusion, then we get into the quantum stuff, the debate gets bizarre. One thing is certain for me though. We need the feeling of having freewill, regardless of whether it is a complete illusion or not.