BF doesn't really need single player these days, in fact it's probably just a resource pit that doesn't even affect sales.
Back in the day, the BF campaign was just a series of bot matches, I preferred that, it gave us the chance to get some practice in without having to go online. They should just go back to that, heck, I played with bots in BF2 a helluva lot more than I played online. Or a LAN game with bots, that would be fun. I've bought BF3 on 2 systems now and never once bothered with the single player campaign, I did do the co-op missions though, they weren't too bad.