#slackisshit
If your company is slack first (not investment advice) then, essentially, slack == mail, so why do can't I turn off things like this.

The smug answer is "because it might be urgent and we should make their phone beep."
Sure, but that's a no-op because there is so much noise from slack that you turn off notification sounds anyway. I'll read your slack message along with mail, when I break to process all my inboxes. Unless it is from my manager. That beeps.