Too many wasted years
Because Hollywood would not give him the opportunities or meaty roles that they throw at his white counterparts from the UK. Here's a guy who gets nothing but brilliant praise for his work on stage and almost just as brilliant notices WHENEVER he gets a major role in a motion picture (the "2012" debacle is an exception). And yet you don't see Hollywood rushing towards him with parts as they do with Benedict C and Fassbenber and even Clive Owen a few years earlier.
Over the last ten plus years he has been the lead in only a handful of films:
Dirty Pretty Things
Talk to Me (he shared the lead with Don Cheadle and had the most screen time)
Redbelt
Endgame (shared the lead with William Hurt)
12 Years A Slave
Of those films only three were American made (TtM, Red, 12) and all of them can be qualified as being more independent leaning than actually Hollywood productions. And the supporting stuff he gets tends to be unsubstantial. In a more fiar society this guy would have far more accomplished collection of films under his belt.
Hell, even Woody Allen gave him a substantial part in "Melinda and Melinda" and he basically never does that for a black actor. But there hasn't been much followup from Hollywood itself. I hope going forward things pick up for him but he can never gets those ten or so previous years back.