Unfortunately some European countries have extremely strange laws about competitions and contributions, and competing for prizes like this can be illegal in certain circumstances. Of course, this doesn't apply to every single country barred from participating at all, but I guess it's easier for S-E to deal with the countries it knows will allow the competition without any problems than it is to get their lawyers to check out all of the other regions. It's unfortunate; I was lucky enough to be able to participate but I've been on the other side of the same problem before and wished they'd let me enter even if I had to sign a form confirming I wouldn't be eligible for the prize.
(Baffled by the implication that Rudy's haircut is unusual enough to be the model for that male entry; there are hundreds of other anime characters which existed before him with similar hair.)
