DTV is a money sink.
You have to fight 3 waves per round to get 300 gold and 1000ish experience. That's about 10 minutes of combat in the tiers that matter.
Tin cans lose about 2000g per loss.
If upkeep was disabled, tincans would get the same amount per 3 rounds, without the upkeep. This would make the DTV servers more appealing.
BECAUSE, it's way easier to grind gold on a battle server. Just go in naked with a wooden sword and die, and browse Reddit vs fighting super hard on DTV for 10 minutes and get 300 gold when you lose 2k.
I'm with the OP here. The grinding gold thing is not a completely thought out argument.
I like DTV almost as much as the chaos of siege, but the upkeep turns me away from it.