A lot of folks want to run tests off a GitHub action I.e. on a server somewhere. Ideally you want your test stack to fit in a docker image. So this does suck for developers in the respect and you could imagine apple releasing a special docker image that just ran safari if they wanted to really make it easy to develop for thier platform.
However, I imagine someone will fill a server rack with cheap old macs and offer and safari mcp as a service…