If you was allowed to subscribe to 10 apartments, the problem would be if say within a few days of subscribing, 2 of them went offline for relocation another left the project and say another had ISP issues. People would then moan that they are paying for 10 apartments and only 6 are online.
Since no specific number of apartments is subscribed to with the premium subscription, VHTV would be stupid if it now specified a number for less money. Theoretically, a lot of the apartments could be closed and the subscription would still not be cheaper.
So it’s a silly suggestion, especially since, as @stanley wrote, it’s also impractical to do.