[Matthias247]

Server sent events are just a potential payload format for response bodies, which allows to encode a potentially infinite amount of distinct messages. Trailers are a different concept since they exist outside of bodies.

If the team had decided to only use http body streams for all payload, they could totally have done that without directly using SSE encoding.

[raggi]

SSE adds another thing besides the body encoding, which is a standard content type that implies unbuffered streaming.