@johnldeboer: Ostensibly for the same reason suns don't explode outward immediately. It's too massive, held in by its own gravity until it exhausts its own fuel/mass. Black holes are not entirely understood but are known to shrink or go "dormant" but then to "wake up" and start nomming again. Infinite anything is difficult to do math about, and "infinite" mass is so especially for us.
@johnldeboer: Black holes keep nomming on things, which is not the case with suns/stars unless things collide with them. Our best mathematical models, as per the late Prof. Hawking, is that black holes will evaporate rather than 'splode.
Research continues.
see: Sir Roger Penrose
He has published some work recently on that very topic.
Others have as well. Also, yes, cosmologists and astrophysicists have made (or mayhaps I should say proposed) distinction between a black hole singularity and the type of singularity thought to be the start of yonder Bang.