The reason it won't change to the top 16 teams league-wide is simply MONEY. Any change to the playoff formatting has to be approved by the team owners (2/3rds I believe)... so why would the east owners vote to have less of their teams in the playoffs when it would cost them money? Besides, the top East teams like having easier matchups in the first rounds of the playoffs... if they were mixed in with the west teams then their playoff route would be a lot harder.
It would be great if the league was able to move towards the best 16 teams making it into the playoffs, but even that can be greatly skewed depending on strength of schedule... east teams still play the majority of their games against other east teams.