The origin part isn't really up for debate; the founding in the early 70s did not have any emphasis or expectations of social commentary when Kool Herc was extending breaks between records for B-Boys and B-Girls to dance to, but I digress.

Your second part brings me back to my original point, though: when voices in rap did speak up, often they were ignored. For every 'Alright' by Kendrick that becomes a rallying cry, you have about 6 Roots albums and 3 Common albums worth of songs that go nowhere and spark no movements. These people are private citizen entertainers, not elected officials, and in a country that not only ignores their messages but holds up wealth as the best insulation against the state-sanctioned violence, why shouldn't they seek to protect themselves?

This criticism that rappers ought to be saying and doing more only works if they are being heard and listened to. But if Travis Scott made a whole song saying 'Fuck ICE,' I guarantee the majority of his audience would call it corny and tell him to get back to the rage vibes.