@mlanger @jakebrake @mayintoronto you're right that there are very few followers for the hashtag accounts on tags.pub. We are just getting this service started.
We're actually pretty careful with bandwidth.
I am one of the authors of ActivityPub, and I wrote a programmer's guide for O'Reilly Media about the protocol. I try to use it as carefully as I can.
If nobody's following a hashtag account, no data gets delivered.