People want to leave X, but they still want the same old, rather than new stuff to make things better as a whole. They don't want to have to do this "pick a server" thing, they want to have an algorithm spoonfeed them popular content, and it would be best for them to have to put in zero extra effort. In Masto you have to put in the hashtags to get found, and search for and follow people and hashtags to find stuff you want, and essentially DIY-ing your feed seems to be too much work for people.