Why is there hundreds of cryptocurrencies, but it's hard to find a platform to invest in them?

A professor of mathematics that I know, analyze Bitcoin, and found it to be primarily banking software crossed with gambling software. Each and all of the cryptocurrencies exist based on one idea but somebody somewhere will think there are valuable. A bit like fiat currency which we all use. However, the whole system is predicated upon a bubble Market that you get out of just before it crashes.

I still don't quite grasp the whole concept of these.

Ethereum is pretty good and has many uses besides being a currency