Safari has tail-call optimisation.

We don’t have it elsewhere mostly because Google:

1. Agreed to implement it [it’s in ES6]

2. Implemented and shipped it behind a flag

3. Unshipped it.

4. Proposed something else [ https://github.com/tc39/proposal-ptc-syntax ]

Prior to that, Firefox had proposed a carve out for cross-realm calls, but then they didn’t bother implementing anything.

While apple is against Syntactic tail calls, they’re mainly just opposed to versions of it that would remove/unrequire the tail-call optimisation they already do: https://github.com/tc39/ecma262/issues/535

For the version of it that is backwards compatible, they wouldn’t need to do anything other than ignore the syntax. Their main concern is that it "could add confusion with very little benefit."

Safari is the mainstream browser with proper tail calls implemented. Was there some historical point where Apple blocked it and so others followed along but then Apple turned around and did it anyways?

JavaScriptCore did not block tail calls. In fact, they were one of the biggest proponents of it because of their Shadow Chicken approach.