They couldn’t get Chao or Meaney quite as frequently as everyone else because of their film careers. I know with Meaney they really wanted to show off his acting skills when they had him and determined that he portrayed suffering really well, so O’Brien suffered a lot. I think Keiko’s problem was that she was only in a couple episodes per season and the focus was typically on whatever horror was happening to Miles that week. She’s not so much a bad wife as a barely present side character.