Lots of places have succumbed to the CYA temptation that today's litigious society has foisted upon us.
Someone who has the legal right to buy a 36' TT but might not have any clue how to drive or spot the trailer must be protected from their own stupidity by warning them ahead of time that the site is old and smaller and their feeble brain and talents won't allow them to get in without smashing it or someone else's unit.
A good friend of mine has a huge 5er and has put in plenty of 'small' sites without any issue at all.