It's because most companies put their heads in the sand when it comes to DVD pressing and still have it done abroad mainly in Taiwan.
It's frustrating because they're all obviously anti-piracy and put money into organizations like the IPPA, but still go to the lowest bidder when it comes to making physical copies of their works. I know a few companies that press in Japan and piracy of their titles still happens, but it's much less and its rarely new titles.