Why would it be? Being open and e2ee is irrelevant for mpost people.

Most private messaging is done in whatsapp and after that telegram. Telegram has spend more usability and less on most other things.

Then it compete with Slack and Teams on the cooperate side, where it was much later and less optimized for it. Slack took much of that market.

It did replace IRC in many places but that was only ever a small part of the market.

Basically between Whatsapp, Teams and Slack most of the market is covered and nobody is really a big player.