Most of the big jets are sold pre painted & I suspect that if they weren't it could be very expensive & very difficult for the potential buyers to find local people who could come even close quality wise for much less cost than what an air frame sells for. Getting most scale jets painted could cost as much or more to paint than a full sized car especially if there are a lot of graphics like Red Arrows schemes etc.
I guess that there are less and less real aeromodelers around these days, and more who simply fly pre-built stuff. ARTF was only just starting to become a thing when I got out of the game, that was back in the late 80's. It used to be that most everybody at the club not only built their own airframes, usually from a kit, but finished them too. The one thing that did eventually disappoint me with finishing them was when they introduced the iron on, heat shrinkable cloth covering. Because I loved the small of Dope when my Dad was covering a scale/semi-scale model in a traditional finish.