It doesn't though. The lifeblood of baseball is the regular season. Teams make their money on their local revenue, both television and attendance, over the course of 162 games. And most teams don't make the playoffs. 3 5-team divisions allows for a greater amount of local rivalries, while 2 divisions of 7/8 just spreads that around more. Your plan only focuses on the playoff end of things. But in the current system divisional rivalries already meet in the playoffs with regularity. The Cubs have had big matchups with the pirates and cardinals in recent years, the AL West is going through it this year. And the hockey thing only happens because everybody already makes the playoffs. You can "encourage" all you want but forcing 15 teams into two divisions and then forcing teams to face a specific team in the playoffs is just making a mess of a system that already works. Again, the bottom line is this system works. It balances the idea of making the regular season matter, having a benefit to having the best record in your league, giving a 2nd chance to a great team that sits behind an elite team, but "punishes" them for not winning the division in the first place.