The Vikings scouting department and coaching staff have spent a lot of time scouting quarterbacks in advance of the draft, thinking that there could be some good choices for them at #14, and maybe later on as well. They didn’t extend Sean Mannion as the backup, and appear to want to go in a different direction with the backup quarterback position.
Most likely, the decision to pursue a backup quarterback in the draft was made a couple months ago, maybe earlier, but since that time there have been developments - most notably the 49ers moving up to #3 - that suggest the draft will unfold in such a way that will make it difficult for the Vikings to draft a potential future starting quarterback.