My guess is Planex's are probably the most returned tool. People buy one to do there house, return it in 30 days. Thus why there are always Planex on recon and always at a good discount.
The CT36 and CT48 have a place I'm sure, but a CT48 is big and now with cyclones, I would think even in shops where the 48 might have made sense in the past, now it doesn't so much. A CT26 with cyclone is only 1" taller than a CT48 by itself. Of course neither is below 36"/900mm bench height. In a non-cyclone world, I guess in a shop the CT48 makes some sense. A bag hold almost twice that of a 26, but only cost 20% more. So there would be some value.
So you have some big vacs that probably most folks don't want now, and a tool that gets constantly returned. I would think festool does all they can to just stop them from piling up on them. Thus the "3 CT48 combo kit" comment.