I feel like there must just be very few vaguely high end XL and larger size bikes sold full stop in the UK.
And decent examples seem to sell fast, while sometimes overpriced ones with obvious problems (stem slammed & steerer tube cut on a bike that fits 6’3” + riders makes it useless to many).
Oddly I’ve seen about 10x as many supersix evo 60cm bikes for sales than I have CAADs - tempting to go for one if a decent, sanely priced one less than 150 miles away comes up.