Slack is an enterprise product. You aren't the guy who buys it, so what you think is irrelevant. They don't care anymore, user experience won't affect their bottom line unless it somehow becomes a Powerpoint bullet vs. some other enterprise competitor, which by definition is equally unconcerned about end-user opinions for the same reasons.
Atlassian is the same way now, providing any kind of feedback to them is equivalent to sending it to /dev/null.
The other thing here is the beauty of a SaaS model once you are an established player. Some product manager inside Slack or Atlassian can upend the user experience of millions of people almost instantly and they can't escape it - an origanization can't just decide to stay on an older version or roll back. Your only choice to drop a subscription for a service in use across your whole organization and which will require going through huge organizational inertia to change. It's ultimately bad for the SaaS companies as well since they never get any real feedback on how their product is perceived (subscription revenue is stable!) until their junk gets so bad that a new competitor without the baggage comes in and suddenly upends the market. Kind of like ... Slack, five years ago. It can happen fast.