[kawa]

Why allows it for free will?

Consider those two situations:

A: You know everything and decide about something based on all the facts known to you

B: You know everything and decide about something based on all the facts known to you plus the result of a random generator

Why is B more "free will" than A? In B there is simply another fact which is beyond your control which modifies your decision. That doesn't makes your decision more free than A, you simply have an additional "input" to consider.

One may argue that B is more free than A because in principle another person with the same knowledge as you would know what's your decision is in A but won't know it in B because of the influence of the random generator. But that doesn't makes B more "free", it only makes it a bit more unpredictable. But in reality it's impossible to always know all facts leading to the decision in A so both have similar unpredictability.

In fact I would consider only A as real "free will" because even if your decision is only determined by (external) facts, it's still all your reasoning based on your beliefs, experiences etc while in B there is a determining factor outside your reasoning you depend on which makes your decision less free (because you may have to decide for a sub-optimal outcome because you're forced by the random generator to do so).