Because it is correct to do so. "Boltar's evolution" would be correct
grammatically, therefore "a million years' evolution" is also correct.

Actually its not. Years is a plural , its not in the genetive case in
that
instance otherwise it would mean "a million evolution of year" which is
clearly nonsense.

Pot, meet kettle - I've known you use pretty awful language in your
time.... if you can't take it, don't dish it out!

I generally only dish it out when other people have been rude to me to
start with.

B2003