These things don't make the rounds on major media, so it's not a surprise you didn't hear about it, most people don't.
This particular death actually received more eyes than most 'cause mma outlets worldwide covered it 'cause the kid came from the former light weight champs gym, Anthony Pettis, and his coach was in the corner. The gym's practices were brought into question as pro fighters who left it began to speak out. I believe there was a civil suit, but i'm not sure what came from it.
A heavyweight pro died this past week and he barely got some mentions, mostly 'cause of his exposure in the UFC.
Part of the sport people don't want to see.