Vince McMahon reportedly did not want to give up the idea of separate brands. As noted, the Wild Card Rule will see 4 RAW Superstars be eligible to appear on SmackDown each week while 4 SmackDown Superstars are able to appear on RAW each week.
WWE has been facing outside pressure from NBCU and Fox to bring the ratings up. The networks will not be happy with how bad the ratings are this coming fall because of how much money they are paying WWE. Fox and NBCU want star power on the shows and there has been a feeling that the brands don't have enough star power individually.
It was also noted that Fox wants RAW and SmackDown storylines on the blue brand show when it goes to their network on Friday nights in October. NBCU was reportedly upset about the recent drop in ratings, especially for the third hour, and they were asking questions about the decline, specifically why they would give away a top star like Roman Reigns to SmackDown. There has been pressure from NBCU and Fox to have the top WWE Superstars work both shows.