That's federal prison, which houses a small fraction of inmates, and for more serious offenses. You need to look at the state stats. In California, for instance, drug inmates make up about 14% of the prison population. Violent crime makes up 44% (actually, it's probably quite a bit higher than that, because "burglary" is counted as a property crime).

To see why the federal statistics are misleading, consider how someone ends up in federal prison for burglary.

Having experienced it firsthand, I wonder if those numbers don't tell the full story. There are whole families basically going in and out of jail running the drug trade. I never got the sense that violent criminals had quite the "revolving door" effect.

Edit: then again, it's likely that drug offenders would be much more open about what they're doing time for. Now that I think about it there could definitely be positive selection bias (or whatever) affecting my perception.

Their door revolves too, but because their sentences are longer and parole harder to achieve, it revolves more slowly.