Why not? I submit that the psychological side/approach/impact is a HUGE determining factor in why games aren't pre-decided on paper. The problem you're going to encounter is that momentum measured at an individual level is almost unmeasurable without real-time CT scans on the players monitoring brain activity, and on a team level things like chemistry and synergy (also non-quantifiable to statistics, but very real factors) are going to play a huge part in whether or not momentum manifests itself in anything quantifiable to stats. Coaches, nevertheless, preach about things like "building off a good shift/PK/whatever", "getting mojo back", "breaking out of a funk", hot/cold streaks, etc. And that's because, if "harnessed", momentum is something that you can build on - even if "only" psychologically.
Because it's possible that any small difference in mental state in some players in the aggregate is not significant. It's possible that the effects are not large enough or they're large but it doesn't matter since they're not good enough to take advantage of momentum or the other team's negative momentum. Social psychology is a very qualitative field that has a lot of subjectivity to it.