The thing is, a lot of developers seem to have no anesthetic sense whatsoever. I realized this when I noticed that almost all Emacs themes are garbage, and that no one seems to mind. I even wrote a blog post about it with several examples and people thought I was trolling.
I mean, just five minutes of work put into this Slack thing would have improved the look a lot, so the other commenter's point about priorities is just kind of dumb. Slack may be a piece of junk but at least it is passable in the looks department. It's not like it's the 90s or anything. How can someone think that looks aren't important?