Well, years back I released an unstable sort called pdqsort in C++. Then stjepang ported it to the Rust standard library. So at first... nothing. Someone else did it.
A couple years later I was doing my PhD and I spent a lot of time optimizing a stable sort called glidesort. Around the same time Lukas Bergdoll started work on their own and started providing candidate PRs to improve the standard library sort. I reached out to him and we agreed to collaborate instead of compete, and it ended up working out nicely I'd say.
Ultimately I like tinkering with things and making them fast. I actually really like reinventing the wheel, find out why it has the shape that it does, and see if there's anything left to improve.
But it feels a bit sad to do all that work only for it to disappear into the void. It makes me the happiest if people actually use the things I build, and there's no broader path to getting things in people's hands than if it powers the standard library.