In recent weeks, people unhappy with Mastodon project talked about forking the project in a different direction. It's harder than it looks.
A lot of people have talked about the possibility of forking Mastodon to get the many improvements their communities need. Making such an effort successful is another discussion entirely.
I don't really see the point in forking a project like Mastodon unless you are already deeply involved with its development. It doesn't do enough that you couldn't rewrite it better (as in in a way you understand better and with lessons from the original taken into account) in the time it would take you to fully understand all the details of the existing code base.
It actually does have that nowadays, it's just that the feature requires Elasticsearch to work, which is one extra piece of infra for admins to worry about.
It absolutely is. Yet, as Sean said, it's also yet another bit of software to run and maintain, and ES is known to be a bit of an effort to keep going well.
Admins having only finite amounts of time and/or resources, might make the very understandable decision to leave it out.