Sure, they vacuum things up, but people have agency. They choose to use platforms. They can choose to use different ones. I can't influence every person's choices, but I can choose how I invest my time and social energy, and present an alternative for people who are alienated with existing platforms (a very large and growing population)
This is a little atomistic view, but essentially in the correct direction. I would also add we need to nurture anti-centralization and anti-corporate sentiments that are still springing up in younger people especially, in their own way. If alternatives could bestow perceived social prestige for at least parts of the population, this would help preserve islands of free discourse for the future.
To be sure, this doesn't mean proclaiming decentralization to be cool necessarily (...fellow kids), but trying to be open-minded and friendly to the public, which I consider to be the actual better part of the ethos of the early Internet era. Being tech literate is "esoteric" by itself, and some complexities and social contracts cannot be really taken away from that, not without going back under the centralized yoke. But even moreso we should be trying to make it a little better by our attitude.
Even if a regulation of protocols for utilities will come, assuming it will be good, we need society to remain willing to preserve it.
But phpbb had its own issues. Many were run by hobbyists who eventually stopped paying the bills or updating the site, and then some bot steals the data or breaks the database.
It's like cloud-hosting email: everyone wants to not host their own email server, but then you're at the mercy of the service provider. For most people its worth it... until it isn't.
Reddit and discord sucked in and destroyed a whole lot of phpbb.