They are two different efforts, started a little while ago, one in Go and one in Rust. I believe esbuild was started first, but they both seem to be maturing rather well lately.
Judging by the commit messages the first esbuild commit seems like Evan moved an existing project onto GitHub while the SWC commit seems like a genuine start. But also pretty unlikely that esbuild was being worked on for 3 years before being put on GitHub so your point still stands.
