@Kinkys-0: Another factor could be that some of these studios have limited appeal, at least to the membership of this site. IMHO, the studios listed in your item #5 seem to have very similar--and thus boring--content: There are only so many ways one can show a 40-ish priest/minister/elder/scout leader fucking a 20-ish twink.
A couple of those studios have a large presence on another torrent site; PM me for information. (I don't want to "advertise" another site in the forum, or to all the world, since this forum is not password-protected.)
@frostycab raised the possibility that these studios might be very vigilant and prone to DMCA takedown requests. If that were the case, then that material would show up on the torrent listings for a while before being removed, and I don't recall having seen that. At least one of the studios in #5 seems to have all of its content on this site.
To quote Yul Brynner...'tis a puzzlement.