Not sure where you got that impression. I recently joined Lemmy after reddit exceeded my tolerance for suckiness and bullshit. I still use reddit occasionally (my 3rd party app still works) and i have only ever seen people posting suggestions to move to the fediverse, not posting that lemmy/mastodon are bad. There is a lack of mature apps (memmy is the only ios one i think) but this will improve no doubt. I think the main long term risk is around funding. Hosting a popular instance will quickly get more expensive as the userbase grows.