Erik Darling explains some of the shortcomings of the missing indexes DMV:
The problem with relying on any data point is that when it’s not there, it can look like there’s nothing to see.
Missing indexes requests are one of those data points. Even though there are many reasons why they might not be there, sometimes it’s not terribly clear why one might not surface.
That can be annoying if you’re trying to do a general round of tuning on a server, because you can miss some easy opportunities to make improvements.
Read on for a few examples of where the results can betray you.