Well, there are some proposals to change this. I'd say it's fixable by technology to some degree. For example instead of a sign up page that directly signs someone up with the specific instance, we could have a more general Fediverse signup page. Maybe ask the new user a few questions what they envision their instance to be. If they're more aligned with this set of rules or the other. If they want "free speech" or a place with more moderation and less argumentative people. And then make some suggestions.
Or instead of just signing them up with whatever instance they visited first, display a list of the current instance and 5 other random ones, shuffle them and make them deliberately click on one of them.
That'd all help. Of course it can't be solved 100%. But we could at least make an effort to do something about it.