A history of poor ops practices and unreliability. In the last year there was one incident where somebody was able to register their root name servers as their own, and another where they stopped resolving requests for a large portion of the internet (mid-October sometime).

From a marketing point of view, I didn't appreciate it before talking to "regular sales prospects" but in our space at least there is a connotation to it. One quote I remember was that we were "a little expensive for a .io".

Ultimately we have stuck with it due to sunk cost.