Vehicles are a Driver and Pilot story
Ground vehicles and the spawn vehicle sit on the Driver track, helicopters on Pilot, and both tracks are fed by exactly the work the vehicle then makes easier: driving teammates from HQ to the zone, logistics runs, and flying supplies in. That is why a vehicle unlock is rarely a dead end — the thing you unlock keeps earning the XP for the next one. Bulkhead's own description of the game names transporting friendlies to the zone as one of the actions that rewards cash, so a squad with a driver who shows up is measurably better funded than one without.