But why willingly introduce extra complexity to the system? Websockets are way less trivial than SSE. Polyfills for a less popular browser seem to be a simpler

But why willingly introduce extra complexity to the system? Websockets are way less trivial than SSE. Polyfills for a less popular browser seem to be a simpler solution to the problem, compared to websockets stack everywhere. Even if I don't have to implement websockets on my own and would use some mature library (because bugs happen even in such libraries).