Yeah the reason for this from my experience on big runs is so that the chase trucks can accomodate parts (e.g. tie rods.) It's a liability and efficiency concern. You don't want to be a moving parts store for multiple types of vehicles.
The other less appreciated perspective is that some vehicles might not be able to keep up, or might be at risk on the trail at the speeds we're driving at (~70-110mph) through the desert with the occasional washout that catches you off guard like this one did for us:
https://gopro.com/v/B25nLm6nZ31X5
The other one we had to consider was range. The TRX's don't have the same range as a SCREW Raptor. They might not even have the range of a SCAB. SCREW's have the 36 gallon tank and SCAB's have a 26 gallon tank I believe, and when you're getting 10-15mpg that 10 gallons is big when you're coordinating 500+ mile runs for 20+ vehicles.