Because in spite of the question ("private host" as opposed to "privacy friendly host"), people have commented in the context of privacy (probably because of the community we're on); and in that context, the mere mention of github or gitlab is met with downvotes.

IMHO using github or gitlab for that isn't much of a concern privacy wise (at least not more than browsing a website from the companies behind those services), but it surely is when it comes to data integrity (which is a totally separate concern, but people often confuse it with privacy, like they also do with security). I would not trust either service with that.