Only players who're interested in GvG have any use for an Observatory. Considering each age map has limited space, I would be generous to say that 100 guilds participate in any world. That leaves quite the number of players who have absolutely no use for one. Also, since it's functions are duplicated by three other GBs that each have desirable other boosts, it's really unlikely there would be very many of the players who do have them who'd be getting them past level ten. I picked up at least fourteen of those BPs...I've had an Observatory forever and it's still just level five.