Not true that there is any sort of official rule to this effect. I've slept in a lot of crew hotels that had only semi-decent curtains.
It is true that well-behaved airlines, who take an active interest in fatigue prevention, do try to book hotel rooms with blackout curtains and good sound proofing. This is however not a universal behaviour and not all destinations where layover is necessary have any hotels with these qualities.
These are classified as "agricultural equipment", and as such they of course have access to most of the road network (not major highways) and do not need to go fast. Only "unnecessary obstruction" of traffic is illegal, "obstruction for reasonable cause" is perfectly fine.
The thing that annoys me is that there is not even cursory control that these cars are used in connection with agriculture. It was fine in the past, because it was relatively rare that the regulation was abused. After a recent change in the law that made it cheap/easy to convert regular cars, it has become a menace.
It is true that well-behaved airlines, who take an active interest in fatigue prevention, do try to book hotel rooms with blackout curtains and good sound proofing. This is however not a universal behaviour and not all destinations where layover is necessary have any hotels with these qualities.