This is a serious problem, that we didn't anticipate during the first reddit migration wave. Since then, we added a join dialog to join-lemmy.org, and tried to make its join page sort by random, to spread out users more evenly.
Unfortunately, the people evangelizing lemmy on other platforms like reddit, continue to link specific popular servers, rather than join-lemmy.org or server pickers that sort by random. And people also tend to just link their own home server as a sign-up, instead of join-lemmy.org, so we'll likely continue to see centralization problems.
We're doing what we can to fight it, but other need to also.
I would love to see some community driven livestreams or events, where we could fund the developers ourselves through donations. We're all refugess from reddit, but that doesn't mean we have to be "libre reddit." I think we could easily fund ourselves if we fostered more of a connected sense of community through events and conversations, turn this group of websites into something more than just friendly social media.
@nutomic recently added Donation dialogs, which adds support for wikipedia-style banners (which are annoying, but they work). I think most of lemmy's problems could be solved if we were able to add a few more full time devs. We currently don't even have a single dev funded.
@phiresky is in the process of adding post tags: https://github.com/LemmyNet/lemmy/pull/5389