Because it’s a public company now. Shareholders demand growth or they’ll just invest in other high growth companies.
Bootstrapped products/companies like Campfire by 37Signals didn’t need to grow, but they also stopped innovating and the chat frature became just a feature inside basecamp.
I think it’s really how companies are structured.
The way Slack was positioned, it also had to grow or it will get taken over by a competitor like teams, or risk getting bought out which is what happened. Maybe the stakes are different when you’re #1 vs #10 in tech!