Get out of your ship and do it yourself.

This, and don't try to come back with the worn out "Dropships cost more" argument, that isn't the issue.

When someone calls in an ADS or tank, it is -1 infantry unit for their team, but it forces 2 infantry on the opposing team to counter that vehicle if destroying it is the desired result. If the opposing team only dedicates 1 infantry unit to AV, then that will allow the vehicle to get kills, while the vehicle is very unlikely to be destroyed, resulting in an unbalanced likelihood of clone loss. One infantry in a DS can also defend an area much more effectively that one infantry, has much more mobility, and requires many more infantry dedicated to retaliating.

You have to pick between higher efficiency but harder counters, or lower efficiency but less effective counters. Vehicles pilots seem to insist on having the best of both. Currently, it isn't as bad as it has been in the past, but there is still a bit of imbalance, imo.

Multiple reasons, mostly the risk/reward factor being off, also many pilots' defence of blatantly abused features over the length of three years or so.