As you can now land a gv anywhere with a little effortand spawn points have nothing to do with a successful landing, why bother?
Because you can land ONLY if no one is around. In any perk plane you can hope to get home and land your scalps. When you spawn your tank to fight at an enemy base, you hardly have a chance to fight your way back home, particularly not if you are in a perk tank. Even at remote Vbases after some time bomb loaded planes will show up, and it's not very likely you can get enough separation from chasing vehicles, which are more than just eager prevent you from getting your perks back.
And the defender can not only land his damaged Tiger on concrete any time, he may also ditch his tank when he ventured away from the base and find himself in an unfavorable situation.
All that makes attacking not very attractive, and even less attacking in a perk tank.