You are shooting your RPGs on the most armored part of the tank. This is your problem.
It takes more damage from the sides and even more from the rear.
Please spend some time using the tank yourself so that you can understand that the grass on the other side is nowhere as green as you think. Especially if you chance on anyone as determined as I can be to blow up enemy vehicles into pieces by any means available , god forbid multiple people who fight them like I do...
Vehicles thrive on the tolerance of the enemy team to their existence. Especially in BF6.