Why do they keep popping up
Because launching a new coin is easy.
and more importantly staying?
99% of them don't stay, they die away, but as long as there is someone to move the blockchain the coin is alive.
Isn't just one or two coins enough?
Who can define what's enough? It's mostly open source so anyone can launch their own coin if they want and that's what people are doing.
Why do we need so many
We don't, most of them will die away, but there's a lot of crypto enthusiastics, developers and opportunists who want to launch their own coin for what ever reason. Some do it for fun or joke, some for serious business, some aiming for pump'n'dump. There are plenty of reasons.
what's the point, what does anybody gain from that?
As I wrote above: some coins push the current technology forward or try to become a legitimate currency and/or business, but most (shitcoins) are just for people to try to make money with them.
It just seems impractical to me and I want to understand it.
No matter how useless the coin is, if it gets listed on an exchange, there's ALMOST always someone who makes a profit selling them, usually it's the dev or miners who get them cheap.
