I think it has to do with data differences between self hosters and data hoarders.

Example: a self hosted with an RPI home assistant setup and a N100 server with some paperwork, photos, nextcloud, and a small jellyfin library.

A few terabytes of storage and their goal is to replace services they paid for in an efficient manner. Large data transfers will happen extremely rarely and it would be limited in size, likely for backing up some important documents or family photos. Maybe they have a few hundred Mbit internet max.

Vs

A data hoarder with 500TB of raid array storage that indexes all media possible, has every retail game sold for multiple consoles, has taken 10k RAW photos, has multiple daily and weekly backups to different VPS storages, hosts a public website, has >gigabit internet, and is seeding 500 torrents at a given time.

I would venture to guess that option 1 is the vast majority of cases in selfhosting, and 10Gb networking is much more expensive for limited benefit for them.

Now on a data hoarding community, option 2 would be a reasonable assumption and could benefit greatly from 10Gb.

Also 10Gb is great for companies, which are less likely to be posting on a self hosted community.