I know why we use it. The API/Integrations are awesome, and they allow us to have a fluid, subscribe-to-what-you-care-about stream of everything our remote team does everywhere.
I'd reckon it was the inbuilt virality it has coupled with all the integrations. No collaboration app comes remotely close in terms of being useful without needing to throw away legacy organisational workflow.
That title was misleading for me - I was under the impression everyone was abandoning it. In this context, exploded is a huge positive.