Because we've tried Teams?

Seriously, though, I don't love any chat app that much. They're useful in some circumstances, but they can easily devolve into a horrific time-suck. People use them for important info that ought to go in emails, for example. Or hammer channels with loads of chaff and the occasional critical wheat kernel, so that you have to waste time on them looking for the latter.

These days, I check mine once a day. I guess that's equivalent to having someone xerox a website for me, but I get a lot more done that way.