For the simple reason that in my opinion it's never "answering a simple question" but more often than not having a chat, with multiple messages and the expectation of responding quickly. The worst offenders are the ones who don't even ask a question but instead write "Hello?... Dude?... Are you there?..." Just state what you want and this will allow me to answer your question in a more efficient way.
I just choose to no to respond until they come to state what they want. Some are offended but otherwise I'm stuck forever.
Teams has it solved much better with a visible "message read" indicator that can be somewhat managed on the reader side, i.e. if you only see the notification it does not count as viewing.
