Every time they were denied by SEC. Feds know that if they accept 1st fund of this kind there is no going back so they will try to hinder and slow this process as much as they can.
NASDAQ were the ones who were denying them as far as I can tell. They were the ones who couldn't be arsed to implement the rule change that BATS is.
And this is how real world finance works. If I remember rightly the first gold ETF took considerably longer than four years. This is probably the world's first financial application rabidly watched over by a bunch of brats who live on the internet.