The schedule maker and, more specifically, the long break between series really did Vegas in.
Vegas defeated Winnipeg in five games, while Washington took a full seven games to defeat Tampa Bay. But then the NHL not only inexcusably eliminated Vegas' earned advantage by delaying game one of the Stanley Cup to May 28th, but punished Vegas for advancing to the final so efficiently.
The May 28th start gave Washington 5 days off, giving them ample time to rest and recover. Not only did that cancel Vegas' advantage, but punished them unfairly. Vegas ended up with an unheard of nine days off between games, just enough time to lose their mojo that has taken them so far in these playoffs.
Because of this it should have been quite predictable that Vegas would be behind the eight ball early in this series. With a bit more puck-luck early on, game four could have had a much different story. Perhaps the thunderous Vegas home crowd will help them get untracked for game five and force a game six. The Vegas Golden Knights have never lost four games in a row all season.
Regardless, it sure looks like Washington has a stranglehold on the Stanley Cup right now. After all, Teams that hold a 3-1 lead in the Stanley Cup Final own an all-time series record of 32-1 (97.0%) since the Final went to the best-of-seven format in 1939. The lone exception came in 1942, when the Maple Leafs rallied from a 3-0 deficit to defeat the Red Wings in seven games.