I do honestly believe that. Every so often there'd be patch notes for dominion balancing items and champions. Waste of time.
Dominion was a no strategy, brainless mode that was rampant with more bots than any other mode ever had. It was nothing like League. At least ARAM and TT had towers, nexi', inhibitors, and standardized creeps. Dominion was a whole different game mode on its own that had a tiny tiny fraction of the playerbase.
Bots are easier to catch on more played games as there are far more reports. Bots were the norm for dominion. Even TT has some bad issues, but since TT is used more, more reports, more catches.
They didn't want Dominion being used as an XP farm for bots. TT and ARAM is harder as players take it more seriously. Dominion? No one cares, you see bots, doesn't matter. It's a silly game mode which is basically a big gladiator arena match. Bots were roaming free because no one cares.
Riot could leave Dominion to appease the tiny 1% or so that actually looked at the game mode once in a while. But weighing that to the cost of having to balance a bit of it as well as the greater amount of leveling bots than others just was not worth it.
There's no point in keeping a resource. It's just bad rep. "Oh, we have this thing called dominion. It's just an empty map that no one uses and we don't look at, but some players will play hide and seek." Ok, what's the point? Delete it and never think of it again.