Many 'old' style Japanese people are xenophobic, and three specific countries worth of people have come to Japan and left a bad taste in their mouth.
Those three cultures are very different from each-other. One is full of scammers and beggars who decided to scam people. A buddy who recently came to Japan early August said "the only people from _____ (that country) that I've met so far have tried the scam me.... that's a pretty shitty representation of their country, especially since that's the ONLY face of it I've seen" and I must agree. While I won't point out the actual country, I will say it is from Africa... and if you look at a map, it's quite literally the armpit of Africa.
The second country is full of loud, boisterous ass-holes. I say 'full of' because this does not apply to everyone. My cereal bowl can be 'full of' milk but that doesn't mean I have no good tasting cereal mixed in there as well. The people from this culture seem to think they own the world and are ass pirates to anybody who isn't their same skin color. Often times, these douche-nozzels are stationed in Japan for a certain set of years and do nothing to respect the local culture. Sorry, but if I go to YOUR country, I respect YOUR culture and don't shove my own culture in your face. If this second country was in a jail, it would be Canada's bitch because Canada is bigger and on-top. Again, this is a generalization, not a specific to EVERYONE from this country for fucks sake
The third group of people are here (by vast quantities) to do one of two jobs....
1) Work in factories
2) Work as hookers and "Hostesses". The internet is full of them and I routinely receive email from these women in vast quantities of spam, asking what my job is, how much money I make and if I want a beautiful young wife to have my children. Again, I will refrain from outright mentioning the country these other 'unsavorables' hail from, but it is another Asian country with a capital city that rhymes with Vanilla. If you want a trophy wife, someone young for you to fuck while you get old, decrepit have nothing to gain in life other than showing off a young sexy wife that everyone knows you bought then you go to this country like so many white men in their 40's and 50's do from the Southern US states. Sorry, but if I'm going to support a wife and her family, it is because I love her, not because I want a fuck-toy and 'rent' her from her family.
So you ask WHY the Japanese don't like folks from other countries all that much? It's because these other three cultures have come to Japan in mass numbers and have a trail of lies, deceit, disease (chlamydia, HIV) and typical 'unethical' (hey, let's not fucking debate this here, K?) jobs. That said, the folks that work as hookers are only half the problem, the other half is the Japanese immigration office and the idiots that work there. While renewing my visa, I sat and watched COUTLESS women from that third country come in, giggle, talk and say how easy it was for them to get their renewed work visa because they are hostesses. Fucking disgusting when I go to university twice for separate degrees and I still am put through more of a wringer than these whores who in my honest opinion are wasting my precious air.
However if you ask people the likes of that user tetsuro, I'm sure he would have nothing but good things to say about the hookers from this country. "They're not all that bad, plus they gave me a discount since I'm such a regular!"