my server got 6/9 of the rewards last SWB, there have been some SWBs where we did in fact get all 9/9, the other servers in our group only have a few people that can compete with our top players(2 of them r stronger than any of us)

as Eplox said, the almost dead servers would be farming alot of easy refines for doing nothing.
so people would want to be on dead servers since those 15 advanced refines are worth 570 coupons, 3X a week means 1710 coupons of rewards a week just from SWB sure they only get 210 coupons from convoy since there is noone to plunder, but thats only a loss of 840 coupons a week for a net gain of 870 coupons, plus the extra rewards from 9tails for less people fighting it and the fact that u can get so many rewards from GNW with smaller groups. In the end it would give too many rewards to low pop servers while high pop servers r penalized.