You keep saying that and that trucks are "pointless micro", but I just can't see how it's true.
Firstly, having them remain as controllable units allows you to move infantry around, obviously.
I have played loads of Wargame in the past. I can't remember a single instance where I used trucks to relocate units. Neither have I ever seen that done by people. APCs yes. Trucks. Never. And Wargame had enormous maps, meaning you indeed need a vehicle if you want to move squads around. To reinforce your ally generally fresh units are brought in since old ones are tied down. Trucks were used simply to drop off cheap units then sent into their demise as scouts.
Having them drive back on Fast Move means you will probably want a safe corridor for them to travel through, which adds depth to the game and makes infiltration behind enemy lines even more rewarding. Having them cost extra, for then to have the player get that extra cost refunded when he returns it safely, gives you an added incentive to keep the trucks alive, and to destroy those of the enemy.
Not really. Battlefield can be vast and when things go down units die left and right, last thing you want is micro manage trucks simply for the sake of managing them.
Even just having them return home as "ghost trucks" adds some challenge to the game, because, as some other player pointed out, then you give yourself away if your troops step off in the wrong spot.
Challenge? It is like going on a shooting range to shoot your guns. Then you have to clean them. It is not a challenge, it is a nuisance. I highly recommend you Act of Aggression if you want to try out gameplay mechanics that are pointless. Whole logistic aspect of that game was to largest extent just not enjoyable.
Then you could of course also have a choice to spawn trucks as logistics trucks carrying supplies, healing injuries, and so on, like in Wargame, and have these trucks come from the same pool as the ones you use to ferry troops to the frontline so they don't have to walk from their spawn point

. Would make trucks even more precious.
Wargame had a distinct separation between logistic vehicles and troop carrying vehicles. While on the ground it might not make sense however, it does have a strategic aspect. You are building a deck of units to bring with you into battle. You have to think it through when you are building it. With multi-purpose units suddenly you remove the need for logistic units and render certain design option useless.