There's a difference between theory and practice. In practice, even a 2+ ton truck such as Unimog can be small for a squad of ten simply because of all the gear.

Look at vehicle qty and personnel figures of large formations. The heads/vehicle ratio is surprisingly small even with the use of many large and outright huge vehicles.

I doubt that 10 men with their rucksack, individual weapon, webbing including canteen and other pouches and helmets fit into any of those "stretched Land Rover" or "stretched HMWWV" on a regular basis.

It's furthermore no good idea to use closed canopy vehicleswithout a substantial qty of spare seats in a unit; some vehilces break down and need to beleft behind at times. Which vehicle is going to carry their personnel if there's no spare capacity?