Hi, I am new to all this, but help me understand this. If there is a crypto coin that is very useful and has functional value, not just speculative, say it becomes very expensive. What is to stop someone from just creating their own coin that is the almost identical to it, and using it instead, so high prices are not paid for the other coin? How can all these coins maintain high values, when people can just create as many new coins as they want?
Nobody, really.
But it's not enough just to clone the coin. You have to convince people to switch to your new coin or at least use it: miners, exchanges, traders.
If there's no gain behind it, nobody will follow you.
There are many Bitcoin clones (and I mean 1000% clones, same algorithm, same everything), then there are lightly changed coins (Litecoin, Dogecoin and many others, changed from algorithm to emission rules). Some have no success at all, some have moderate or even big success.
The coins are not the same because each of them serve it purpose. When you go to coincap.io or coinmarketcap.com you'll see many coins, of course. But every coin there has a features and purpose different from one another. They are actually not the same because they have different purposes, developers, platforms, communities and user-base.