There are currently 20 replies here, and of those, 19 didn't read your question properly and just answered with a different email provider. I know there's a trend on HN of people commenting without reading linked articles but this is particularly bad. It's a short question on this page. In answer to your question, this is a multifaceted problem that comes down to: what do I use email for and how else can that work. I…
Up voted because I'm one of the guilty people you mentioned I wish there were a standard of sorts in im space. It's not signal because it doesn't allow for saving conversations.
As mentioned, there's XMPP.
As well as Signal, there's also Matrix.org which is used by Riot.im.
You could argue there's now too many competing standards (ActivityPub has some similarities in a way too), but without having ever implemented an XMPP client myself, seemingly people had enough issues with it for there to be significant traction given to replacements like Matrix.
Personally I was always a fan of XMPP, and the idea/concept (just not the implementation) of Wave really excited me at the time. Momentum behind XMPP seems to have slowed so I've been giving Riot.im a trial. Sofar I really love it, so I'm once again hopeful.