a) Like charges repel, while like masses attract. Thus it is hard to bring charges together, and it would take an infinite amount of energy to concentrate charges into a point.
b) A black hole is more complex than just a huge mass squeezed into a time volume. Because gravity alters the way inwhich time and space are defined, a black hole is not a mass squeezed into an arbitrarily small size. Rather one gets a horizon formed at a radius of 2GM/c^2. Because electromagnetism does not involve space or time alterations, you do not get the same thing happening for charges.
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