Microsoft didn't force that, they reflected it. Microsoft just made their software facilitate what users actually wanted to do. They don't care about all that tedious effort to scroll and selectively trim and indent and format quotes for a neatly curated conversation. They just want to start typing. They just want all that junk out of their way. Microsoft merely reduced resistance to what users were already finding natural to do.

Email was built as a digital version of snail mail. I guess good old mail services are conversations in a way - but both snail mail and email are more for sharing information than having a written conversation.

Sort of like - I'll send this piece of information out, and maybe I'll get something in response. Maybe I won't.