In the commercial AC world we'd just go down to the supplier, get a reclaim bottle, connect up a reclaim pump and remove the charge, then return the bottle to the supplier and thats about it.
Being a class A2L refrigerant its considered mildly flammable and you'd probably need a special reclaim unit (encapsulated/sealed motor and electrical to minimize risk of explosion or fire if the recovery unit were to leak) but they do exist.
I'm assuming it's only because the dealership lacks the tools/training to conduct the work and/or it may not be legal for them to do so (laws are weird, you do four years of training and cant work on a car AC but a mechanic can do a few weeks and is allowed to go nuts). I'm not familiar with the relevant rules and regulations for the automotive side of the business. You never know, maybe they're not allowed to use anything but those all in one machines legally.
I think its because in the automotive field they have this idea of reclaiming and reusing refrigerant, making all the refrigerant they use "contaminated" really. Though i suppose you dont get bad burn outs in automotive like you might in other systems as there is no motor present inside the refrigeration circuit.