Yeah I know, however when you reply to someone from a notification you just want to reply.
Also, when you move up the context on a Lemmy thread you see each comment and all its other comments. If the comment chain you're replying on isn't the top thread, then you get cluttered up with all the others. On reddit, context meant you only saw the comments that directly lead to the comment you were deriving context from. Furthermore, context was derived from the comment URL with a ?context=3 suffix, so you could easily specify how far up the chain you wanted to go.
Lemmy does context differently, but I prefer reddit's method.