Because in today's NBA, he doesn't need to be a "20-10" guy and an "8-6" might be just fine. Those numbers don't mean as much as the some of the advanced stats - for example, his true shooting percentage, which is probably better than EFG% given that he is a center, is a woeful 45.6. However, when Bynum is healthy, motivated and in the right system, the guy has shown that he can put up 60-handles consistently and rebound at an elite rate.
He is just 26 years old (in October) and seven feet tall. Just about any contending team that can afford him can use that. He may never be the guy who averaged ~ 12 rebounds per 35 minutes played. But with his size, strength and track record, he will garner some interest. Hell, I hope Golden State looks into him.