As someone else said, you have to remain 100% private. The second you become publicly traded, that’s it.
Even then, if you want to make a difference in an established industry, you all but require preexisting deep pockets or some extremely disruptive technology that can’t be easily copied.
You then have to remain steadfast in the face of the ridiculous money that will be dangled in front of you to be bought out.
There’s a lot of stars that need to align.
To chime in on the user creation thing:
I think it’s a natural part of decentralization that it’s harder for a single instance to get big enough to be the “go-to” for general users.
Having said that, I also think this will naturally happen over time. As long as the mechanical aspects of sign up are simple, it’s just a matter of users of a given instance to promote their instance.
World events also always play a role in encouraging a move to freer waters. Look at what happened with Mastodon and Bluesky (though Bluesky imo is just a big snooze button on a blaring alarm)