>>101301424
I feel that's mainly because of two reasons:
1. Wh40k wasn't mainstream when Space Marine came out, in 2011 was it. So a lot of people passed up on it
2. The final boss being a fucking QTE soured many people's perspective on the game's singleplayer story
3. The multiplayer being fucking peer-to-peer sucked ass and caused massive lagspikes for a long time, until they kinda sorta managed to stablize their netcode
I know that was three, deal with it