I have a couple of reasons
1. If fighters went away I wouldn't play the game anymore.
2. I hate tanks and always have. They are slow, driving them is boring, shooting them is boring, camping is boring, I just don't see the action packed excitement sitting in a tank pushing a trigger. Just my preferences.
3. I only have a small amount of time when I play. I'd rather be in the sky than driving around. I'd rather have an intense fighter fight than spawn camping noobs sitting still and quiet.
4. TTs take the majoirty of people who would up in a plane and transfers them to an area where they are not in planes, there is no darbar for tanks, so you don't really know how many people are fighting. The map looks dead. The map doesn't change because there are less fights in the outskirts because the majoirty of players are in tanks in TT, not visible on the map.
5. The majoirty of new players join the game for fighter action. If there is no appearance of fighter action on the map, they will log.
6. Basically you coupe up most of the players in one spot with no radar, or indication of a fight, there is little fighter action, no base taking to create fights, and the tankers aren't providing any support to the base take/defense part of the game.