what kept you? = what took you so long?

2:34 Michael, what kept you? マイケル、何やってたのよ！

Knight Rider - Kitt vs. Karr | NBC Classics
https://www.youtube.com/watch?v=INO6vkYh-5I  4:26 what kept you? もっと早く助けてくれよ！
highlander macleod vs kurgan

参考リンク
http://bridge-english.blogspot.jp/2015/12/what-took-you-so-long.html  what took you so long?