This could be due to people do not understand that camiones is a Spanish word meaning buses. Camiones + co.uk extension may only work if someone develop a transportation website focusing the UK market but providing information on Spanish related content. At least from my point of view.
I dont think it makes much sense to put a spanish word on a uk extension. Despite the commercial and touristic relations between spain and the uk, if I was really interested in trucks (not buses tw, trucks) I would probably look into an .eu extension not a uk one.