The key to it was having everything go through their servers, to their client app on the phone. The problem is that more messaging apps came to prominence (What

The key to it was having everything go through their servers, to their client app on the phone. The problem is that more messaging apps came to prominence (WhatsApp, Slack, arguably instagram and snapchat, etc), they wanted to own their UX and didn't want messages coming through their service to get munged together into a generic feed through someone else's servers and into someone else's client app.