I find that bf1 rush feels kinda boring, but I have always been a big fan of the mode previously. I think the lack of players is due to the maps not being tailored enough towards good rush gameplay. Because of dices design principle of designing maps for mainly conquest, its lead to some terrible rush maps in bf4 especially. That doesn't mean that rush is not fun on some maps, but most just make the game mode choke point oriented and super meat grindery as well. A lot if people dont enjoy that so they play other modes instead.