The script is written, and the actor is either A) asked to play a role, or B) sucks some dick to get into that role.
If any actor plays the role of a 'snitch', they read the script before hand and decided to take that role.
So I guess the question you really want answered is this:
Why do rappers contradict their words by their actions?
and for that my friend, you might as well start bitchin' on youtube hoping somebody notices, because as far as the Big Picture of business and money goes: don't nobody give a fuck.