I think the issue is that crewmen use it like a faster tank when it's role is actually quite different. It's a support vehicle meant for moving troops, supplies, and injured back and forth whilst its' armour and light weaponry allow it to survive and repel attacks from skirmishers behind the front. Its' speed means it can outmaneuver or escape from anything that ambushes it, unlike the Longstreet tank which requires an infantry escort to shake agile T1s and Lurkers off of it if attacked. Still, many people don't realize this and park it at a barricade chokepoint, having it's relatively fragile armour, not meant for sustained fighting, chewed up; blocking Marine fire and movement despite not having the tank's heavy weaponry to make up for it.
Although, LynuahSororitas is right: The maps are small enough that even with many QoL updates to allow vehicles to navigate them better, they still feel cramped and even in exceptionally open areas (like the stretch of land between the Marshall's Office to the Bar in Solaris Ridge) you can only drive straight in top gear for a few seconds before either stopping for or ramming a stray unga in your way. Larger maps for vehicles, though, would probably be at the expense of the xenos and infantry who would both take longer walking anywhere and have to fight in empty, open space. Still, if we're tossing ideas around, I would like to see M56Ds on each side of the transport APC, being weaker and lacking the IFF capability that the frontal gun has, which could be manned by two ungas inside giving it a 270 degrees coverage if you have enough people; greatly differentiating it from the trucks you find groundside. It seems that the current code used for the vehicle weapons could be applied to this but I don't know, everything related to coding in BYOND is much more complex than it first seems.