The St. Louis Blues never seem to do anything you might expect them to. For many years, they kept drafting goaltenders even though there was never really a need.
The Blues seemed to take the NFL approach that you can always use an extra body in that position, so if a good one was the best available, they would take them. Defense seems to be taking that mantle in the Blues mock drafts.
St. Louis does not have a pressing need for a defender, but the majority of mock drafts we have seen so far have the Blues selecting a defender when their name gets put on the clock.