People don't necessarily want to focus on the objective. It may be what is needed to win the game, but what if they don't care, if they find the objective unfun ? (don't tell me that in this case they should play another game. No other game will have the same gameplay, even if that's a similar one. And I'm talking about gameplay, but actually even the sounds can play a big role)
Also, keep in mind that if your teammates don't focus on the objectives, neither will the opposite team. Actually, if you focus on the objective, you'll tend to win much more often.
"Yeah but since others don't focus the objective, they keep chasing me"
That's part of the game. When I think "War Thunder" I personally think "planes", so let's take as an example the objective where you have to destroy gound units to win. The goal isn't all about destroying ground units. You're also supposed to defend allied ground units, and for that, you need to chase other planes.
A player that really works towards the objective will do either or both of these :
– use a bomber to focus ground units, and use the turrets to defend against fighters
– use a fighter to take down other planes, and occasionally destroy ground targets. And it doesn't even have to always be bombards. Taking down fighters helps defending allied bombards, which helps destroying ground targets.