Probably because the content from "gangsta rappers" doesn't instigate brutality that leverages a power imbalance the way cultural and systemic hatred drive police brutality.
> thug brutality is a bigger problem than police brutality
It's objectively not, and I won't hide the reasoning either: police brutality is the end result of power-induced amplification of (as noted earlier) cultural and systemic hatred against minority/protected classes. "Thug" brutality on the other hand... isn't even a thing.
p.s. Your implicit analogy between "gangsta rappers" and "thug" brutality suggests you see "thug" and "black" as analogous; not sure if that's what you were going for, but it certainly reads that way. And since you're asserting "thug brutality" as being worse than power-imbalanced crime - more specifically since you're stating your perception of black-on-black crime as worse than police-on-black crime - it's important for you to understand why the movement itself is so focused on police brutality and systemic bigotry. Circa 2016: https://www.usatoday.com/story/news/nation-now/2016/07/27/wh...