I feel they underestimated what the MVP really is and started touting Matrix as great before it was really there, which has backfired and led to disappointment. They also went a bit too overboard on the overgeneralized idea of it being "a decentralized eventually consistent JSON database", which led to a lack of focus on its concrete usability as a chat system. I still use it and it's not bad in some respects, but it's a long, long way away from being able to attract a mass of ordinary users.