Why are there different sized black holes? If they all contain a singularity with infinite mass, one cannot be more infinite than another. So there must be finite mass. Maybe there is a quantum particle that is only mass, with no spacial dimension, such that an infinite number of them can occupy a single space, and that a sufficient density of them will form a black hole?
It's not that black holes have infinite mass. They have infinite mass density. In other words, if a star 6 times the mass of our sun dies and forms a black hole, and that black hole collapses down to a singularity, then all that mass is contained within a point (infinity mass density because the volume is zero). Same with a supper massive black hole which has 5,000,000 times the mass of our sun. All that mass is contained within a point of zero volume. So, infinite mass density. But the overall MASS is not the same as seen from afar. If you are orbiting the first black hole by a distance that is greater than the radius of the original star before it became a black hole, you would not notice any difference between that original star and the black hole. The gravity would be the same. Your orbit is well outside the event horizon. But if you orbit at that distance around a super massive black hole, you would probably be within the event horizon (didn't do the calculation here but just as an example), and you would be unable to escape. Does this help?