Why do some アニメ pick out English names for the characters instead of Japanese names?

It depends on which company owns it.They probably think that the little kids won't understand the names.

There are some アニメ like Case Closed/Detective Conan where the American distributor changed the names to English names because they thought that made the 表示する もっと見る acceptable to US audiences.

There are also アニメ like Cowboy Bebop and Trigun where the characters have non-Japanese names from the start. I suppose that's because the characters aren't from Japan. Bebop takes place not in Japan, but in outer space, and Trigun on a Wild West type planet.
This is all my guessing--I'm not a professional "Answerman" (Or Answerwoman) like they have over at アニメ News Network.