when i was on the feed bulkers my lorry was washed every night with no exception , my tractors were the same , i had an old amunition case in the cab full of cleaning kit & it was used regularly
i feel there is a trend towards keeping vehicles clean nowadays , wether it's tractors or trucks . years ago tractors were tools to be used & they were certainly used & abused ,but about 20 yrs ago the trend changed with the introduction of electronics & farmers sons not wanting to drive rubbish.
it's a psychlogical fact people feel better driving a clean vehicle than a dirty one