I just got an e-mail from the host of the aforementioned challenge that my entry was disqualified for not being famous enough. It was a a monolith from Romania, called the The Sfinx, which is pretty famous there (I think at least half the people in Romania heard of if, and millions had seen it).
Just because the host never heard of it is, IMO, not a reason to disqualify it.
If you look at the entries in that challenge, at least two thirds of them are totally unknown to most of the people outside the country they are in. So by using those standards, the majority of them should be disqualified.