It's because they translate from Japanese into Chinese and then into English. Additionaly because both Japan and China use the same characters in their traditioanl forms of writting... but with different meaning, it ads confusion to their interpretations. Also these are usually just pirating rings who don't give a crap about Kamen Rider and are just in it for the cheap fast bucks. Thus even though they could solve the problem by remembering to use the Japanese interpretation since it's a Japanese show, they don't.
"Oh Hello Chinese man! you speak Japanese and english? Great! Translate this! No you don't need to know wahts it's for. No we don't care that you're not fluent... do it anyway."
It's probaly even worse than that. They give it to one guy who knows japanese so they can sell their bootlegs in Hong Kong, then once translated pass THAT version to someone else entirely to do the English version. Also I reiterate the whole not caring thing.
That's why groups like Century Knights and TvNihon are so great. They acctually care about what they're translating and are putting it out free for Download.