> I don't quite get your point here. Suppose I write a compiler to compile Scheme to WASM. I would have write it so that it does proper tail calls, otherwise it wouldn't be Scheme. What's stopping me?

Stack overflows are stopping you, if you implement Scheme calls as Wasm calls.

In Scheme, tail call elimination is not merely an optional "optimization", so the compiler can't opt to not do it when it's inconvenient.