Email has the stigma of all the junk/grey mail, spam and scam attempts that come in via it - people want to not have to filter through as much of that and for the most part these chat apps solve that problem.

It doesn't help that Outlook's search capabilities have gotten effectively useless - I can type in search terms that I'm literally looking at in my inbox and have it return no results, or have it return dozens of hits without the search terms involved at all. I don't have that problem with Slack or Teams.

However, I think you are right overall on email being better overall for what people end up using chat apps for.