@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.
@thedisasterautist Earth will be long gone before Hawking’s theory can be proved. 😉 I have trouble with the singularity theory of the start of the universe. No one can define, without using infinite as an adjective, what a singularity is, and astrophysicists maintain that at the heart of every black hole is a singularity. Must be a different kind of singularity than that which started the Big Bang, I guess. Or maybe every black hole will eventually have a Big Bang and create a universe.
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.
@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.