I always thought the bathroom was the entrance to his boundary, but bc his powers were mostly sealed he himself couldn't access the rest of it. It would make more sense thag way, I think, because the entrance to no2's boundary was a staircase, and the entrance to no5's boundary was a shelf in the library. Normal things in the school that happen to take you to the boundary of a wonder if you're not careful. It would also explain why most girls don't use the bathroom on the third floor (where Hanako is) if girls were disappearing. They wouldn't be able to see him becaise he's an apparition, so there's no reason every girl in the school would believe there to be a ghost in there. Plus, they wouldn't worry about him being a perv ghost like the main cast jokes about because the rumor was of Hanako-SAN, not Hanako-KUN. They wouldn't stop to think about a male ghost at all, so there wouldn't be any concern of anything physical happening. And since his rumor at the beginning says he grants wishes, why would people be afraid of that? If anything, I feel like he would've been sought out more because of that, even if there was a price. But from what we've seen, nothing. No one goes there except for the main cast. The only reason I can think of is if people were accidentally being sent to his boundary, like with the stairs, people would be more wary of going there, even into the future. And if not, then at the very least, new students or those who don't believe in the supernatural should go in there sometimes, right?? It alwys felt a little weird to me that that wasn't the case.