A best of three playoff will never happen. Not enough revenue will come in for the teams. The owners and player's union would almost certainly demand a five game series.
Of course, rarely does a series start right after the season ends. This year, for instance, there was a one game day off.
One day.
OK, now we have two games in the first city.
Three days.
Now, we have a travel day.
Four days.
Let us now assume that all three of the games will be played in the second city. Highly unlikely - but let us assume that, anyhow. So, we have three more games.
Seven days.
Of course, the next round of playoffs certainly are not going to start right after the end of this round. In fact, there is usually an extra day off in there for someone - after all, the playoffs are staggered so that all games in a certain round are not played on the same day. Add a couple of more days.
Nine days.
That is nine days off for the team that did not play the first round. Not a welcome three day break - a very long nine day period of inactivity.
While this might not be a big deal in football, where teams with the record do get first round passes, baseball is a bit of a different sport. A lot more finesse is needed - finesse which demands a lot of practice and a whole lot more day-to-day action. Practices and workouts are no substitute for true in-game situations, and I fully believe any team in the big leagues would rather play another ballclub during that period, than sit around and see their edge go away.