Called seatgeek once to ask somewhat of a similar question I guess during the regionals last year because I couldn't sell my tickets as an entire series but only certain individual games. They said that the host of the event has the authority to decide who, when, and how tickets are made available for sale on their platform. I asked her then who are the types of folks that get that level of access and she said often times the event host will allow certain brokers or even the event host themselves to sell tickets in a manner that the general public does not have the same access to.
Some objective reasoning would lead you to a curious conclusion as to "who" is selling when you see an entire row across a section available for purchase and the quantity is significantly more than the 12 tickets per section limit in place on donors.