We don’t need infinite content for every niche so you can scroll forever.

Having critical mass in niche communities (like Reddit does) is not important because of “endless scrolling”, but because without it the Fediverse will always be seen a second-option. If the 90/9/1 rule is to be taken seriously, this means that 90% of the people browsing Reddit would have no issue to go to a mirror to lurk. If then half of these 90% are getting their posts from a mirror, the content creators will quickly realize that their audience is moving on another platform and start posting there.