Slack but better UX/pricing, sure, but the real reason everyone is on Slack is network effects and integrations. External partners force you onto Slack even if you hate the pricing, and there is other lock-in (CI/CD webhooks, monitoring alerts, support ticketing).

I like the concept, but there are reasons why everyone doesn't just switch to something like https://once.com/campfire which is self-hostable and completely free.