A training operation only needs one motorized vehicle if it uses W.and D for the C+E candidates.Its therefore cheaper to run this way, you wont get a D on your licence as that is for buses.
I already had my artic licence when my company gave me a course on W&D in the 90’s, on the A-Frame variety, let me tell you, it’s easier to reverse an artic than one of those 
, the ■■■■ things have a mind of their own, I did master it well enough but they are very unforgiving going backwards 
Phil
I passed in a traditional artic outfit, did about 2yrs driving artics, then got a job driving a wag + drag outfit (b+q) doing demountable boxes (drop 2 boxes, drive out, reverse under 2 boxes) which is probably the trickiest thing you’ll ever do in a wag+drag? and had no problem whatsoever doing that, so can’t see why anyone would struggle the other way round?