So I had the flag and was all by myself at the cap fighting off like 6 enemies while my team did fucking nothing to help me I am mad.
Get used to it! For now.
Until they add custom server support, building any sort of community with decent game sense is hard. Right now with the quick play only, it's comparable to the level of play in TF2 quickplay.
Luckily that is their next "big thing" to implement, so hopefully soon-ish.
Usually, if your team is nowhere to be found, go hide with the flag in the generator room, in 75% cases, thats where they are hanging out. Or just keep running, avoid turning sharply and don't go down the same slope you used to get up, because there will be chasers, and they know how to deal with that tactic.
Also chasers have extreme tunnel-vision on the flag carrier. Try to steer them into your teammates (if possible), not away from them.