There sure are a lot of them ...

A simple categorization can be done by separating them according to the number of dieties in which they profess to believe. In my "regular" profession as an IT professional, the important "count" mechanism is zero, one, or many. Most computer systems that deal with data relationships have to deal with these three different cardinalities. Oddly enough, that seems to me like a good categorization element for religions.

In the "none" category, we have religions such as Buddhism (Buddha is an "enlightened" being, but is not the progenitor of the universe), Taoism, etc. Some people argue that these are not religions, but philosphies. But there are Buddhist  and Taoist temples, and, more importantly, they are granted the tax-free status here in the US with which other religions are favored. I'll accept them as religions for the sake of this entry.

In the "one" category, we have religions such as Christianity (in many different flavors), Judaism, Islam, etc.

In the "many" category, we have the ancient Greek and Roman religions, Voodoo, Santaria, many of the American Indian religions, Wiccan, etc.

So, back to the essence of the question: Why are there so many?

The answer to this is deceptively simple. But it can only be recognized by answering another question: "Which one is right?"

That is the subject of another post...