tour buses with 2 floors and big buses are the ones they banned. I think vans or mini bus are still allowed. I have seen so many news about big buses accidents; turned over and lot of people died and got hurt. I think that’s what they try to prevent.
long holiday = could be a “a lot of people“ and the traffic could be heavier “than usual”. As I know especially on Buddhism holiday a lot of people are going up there to make merit. So maybe that’s why.
They do not allow “big tour buses “ to go up because it’s dangerous ( lot of people and rainy season ). You can still going up there by motorbike, red truck, car, etc. Doesn’t mean you cannot go up there at all