Wow, bun support was just added in November last year (I think). That's a lot of work to throw away, but you can't argue with their reasoning.

bun is still supported for specific versions so nothing is being thrown away. in any case the actual code is the same, since it's all javascript. it's more a matter of the wrapper code that calls the different runtimes and maybe some edgecases where the runtimes are not 100% compatible.