The idea would be to not add barriers to entry for new users or require servers to advertise/add barriers to entry themselves.
I think we should ask the reverse questions;
Why should severs have to manually advertise themselves and manually erect barriers-to-entry (which are both crude/slow techniques for hitting a target number of users) when Lemmy.world could almost instantly send them all the new users they desire, stop exactly when they’re full, and do it in a completely automated way?
Why should new inexperienced users have to deal with barriers to entry and then have to search around for some obscure Lemmy instance on their own, when we could automatically guide them to an obcure server looking for new members?
New servers can still use their old/existing methods, but if they want they could “opt-in” by asking to be on the recommded-server list of Lemmy.world (or whoever)
Getting on the front page of Google is hard and Lemmy.world has done it. Instead of that achievement working against us (and having to manually tell/confuse people saying “please don’t just sign up for lemmy.world”) why not leverage that achievement to create a maximally-distrubted system. Cause we can eat our good-user-experience cake (Google “Lemmy”, click on the first link, put in sign up information) and still have our dont-put-everyone-on-one-server cake too.