[dudeofx]

I am looking for a technical explanation.

Would this be because of fear of establishing a precedence where if a lot of people did that you'd have a situation of a lot of leechers but few seeders.

If thats the case, its the same situation where you have a lot of users watching videos on a server. The server can limit membership to protect itself I suppose but a personal instance would be better then a user that just watches but does not contribute.

I suppose somebody could make a RPI client that becomes a member to one or more instances and just downloads. Just let the servers protect themselves by limiting use here and there.