Once you don't have to worry about not having to pay rent, not having to pay electricity etc then your appetite for risks grows. To get to that point you either need to start from a rich household (parents) or get to a certain age, have some money to support you (from previous work) and then go into entrepreneurial experiments. This is a big reason why you see older entrepreneurs embarking into that journey.
The additional problem I see with Slack is that their calls/video chat option is really inadequate and almost everyone is opting for Zoom. Zoom + Slack is a very steep price point for a lot of companies, especially in an era of cost saving and insecurity about the future.
My company opted to move to MS Teams because the experience is better as it integrates calls + chats and we were already using office365 for emails and documents anyway, so it was "free". As someone said already, it's hard to compete with free.
I can't see Slack getting out of this in one piece. I see Amazon being the obvious choice here.