If 99% of the network is meta (probably more) then every user will follow stuff on meta instances, instances like Reddit, will have an enormous load of content. You don't need "everyone following everything" to get that, just imagine a "Reddit all" instance it will bring any small network to its knees.

It's all in the numbers, and the usage IMO. I don't want 10000 soul less posts a day, I want to see what people are up to, working on etc. those concepts are quite incompatible, at least on Lemmy because we are just small servers, not a uniformed giga billion network.