It’s a GAMA thing. Wheels Up, until the purchase of Travel Management Co, did not have an operating certificate. If you have ever attended a Flight Safety course on the king air you would know that they teach every single check in the book. It is a company thing. When I flew King Airs part 91 a long time ago we did the extensive checks only occasionally. Actually maintenance did a lot of them like vacuum and pressurization checks.
One reason is that these aircraft are away from maintenance bases for a long time. The extensive checks find the problems when they occur. Many part 91 operators get the airplanes back at home base every night or every other night and they are able to do these checks by maintenance or in the hangar.
It’s just the way they do things there.