Answer: Because they hit a ton of home runs.
Question: Why did the Tampa Bay Rays lose the World Series?
Answer: Because they did not hit a ton of home runs.
It's passé in baseball to harp on doing the little things during the playoffs: bunting, sacrificing, hitting to the right side, stealing bases, etc. If you do these things well, the theory goes, you will be successful in October. Yet time and again, we find that it's the team that out-pitches or out-slugs their opponent that emerges victorious. That happened again this year. The Rays simply ran out of slug, and when they did, they lost.
In fact, they lost despite stealing a record number of bases and scoring on not a few small ball plays. That's the irony of the whole situation. I'm sure not a few columnists will take the time to point out that home runs are fickle and that the Rays simply relied on them too much to be a winner. The problem is that this is true of virtually all teams, even (or especially) championship teams. When you don't hit for any power (with men on base), it's really tough to win.
Naturally, if someone could find the fountain of hit-home-runs-all-the-time, they could practically guarantee success in the playoffs. Since this is reality, where chance governs so much of the events that make up sporting events, sometimes the power just doesn't come when you need it. So it goes. All you can do is put the best team you can out there and hope that you get some breaks. That's not a flawed strategy or one-dimensional approach to the game. It's just The Way Things Are.
Hit for power and win; don't hit for power and lose. That's the lesson of these playoffs, even if the talking heads decide that the exact opposite is true.