You are trying to try people what they should prefer. This is about openness and choice. If I've been using screen and irssi/xchat/etc for decades I don't want to learn anything new. I don't want a huge app shoved down my throat that's not nearly as customizable and integratable into my workflow as all those tools I already know. The slack app is just a horrible tool designed to get into your way and interrupt your work. Thank god we didn't jump that shittrain on my current job.