MLS would have a tough time using the table format. Americans are too accustomed to the playoff format so a table format would be tough to market. The closest to the table format is college football but they still play a championship game and every season there's controversy on who plays in that game!
Second, there's no relegation in MLS. I won't get into that detail, but relegation would be very difficult to implement in the U.S. due to how physically large this country is (MLS tries to be geographically balanced), how much investment is put into new soccer stadiums, and the franchise entry fees...
Without relegation, a team at the bottom of the table wouldn't be motivated to play hard because the season is lost already. With a playoff system, the team can believe they can go on a winning streak and just make the playoffs.
MLS has modified the playoff system this season to favor teams who do well in the regular season, but it's not close to a table format. Without relegation, I don't see the format changing.
I believe the playoff system saved the Mexican Primera League. They were having financial problems until they implemented the Apertura and Clasura "half seasons" with a playoff system at the end of each half season.