There are many good reasons why people don't feel enticed to play the objective but here is the one that I think is the biggest right now.
Domination is setup completely wrong in this game. I have said this before but will try saying it again. When you place all of the flags in a line and force teams to have to secure B flag to win, you make it like shooting fish in a barrel and noone wants to run in repeatedly to their deaths. Honestly, with the way they set it up, you don't even need A/C flags in the game just B flag. Respawns alone will guarantee you A or C in EVERY match. Saying play the objective in this kind of domination is like saying, jam your hand into the spinning blender blades.
You need a triangular flag layout in domination so that people aren't forced to go one way only.
And your name is "Family Team"...hahaha Okaayyyyy
The guy who said the comment you dis-approved of, is actually right.
While in the perfect online world, people would adhere to norms that are considered "fair or right"...the online community is far from the perfect world and in-fact lacking more "perfection" than real life.
You did not buy his game. Until they decide to have dedicated servers, admins who control gameplay in-game, or a setup where the game auto-kicks for gameplay deemed unfavorable....that person can play how they want (as long as they are playing within the rules/confines of the game itself).
While this FACT, may be unfavorable by you people...it's still FACT.