Because I think it will draw attention to the game more. The week before the Super Bowl is one where everyone wants more football. The game will have a lot of eyes on it, and the city will already be prepped for it.
It does take a few elite players from the game, but it'll give a few other guys a chance to get the spotlight on them, on a stage where I think people will actually watch.
In some ways it is better. The deserving players on the two teams will still be voted to the pro-bowl and in many ways being voted to the pro-bowl is a bigger honor than actually playing in the in the game. And any NFL player who would rather play in the pro-bowl than the superbowl has absolutely no concept of "team." Likewise fans of the two superbowl teams are not gonna be majorly bummed out because there favorite player is not playing the pro-bowl. Or if said fans are than they have a serious case of only seeing the glass half empty.
I do see some downsides.
The coaches for the pro-bowl are the losers of the NFC/AFC games. Under the old system they had a couple of weeks to recover from the long season, the heart breaking loss and have some time to spend with their families that they have barely seen since training camp before needing to turn around and coach some players they don't really know. Now they will expected to go straight from losing the championship game to coaching the pro-bowl without even having a chance to spend a day with their families.
Sometimes players from the defeated superbowl team skip the probowl for much of the reasons in the prior paragraph particularly if they have been to the probowl before. Players that have had a couple of weeks to relax since their last game even if it was the championship game tend to show up no matter how devistating the playoff loss was. If we have both the championship winners out and the losers skipping that means that we are lacking players not of just the two best teams but the four best teams.
Plus moving the pro-bowl up three weeks may result in players that weren't seriously injured but banged up not going to the game because they haven't had a chance to recover from the bruises. Particuarly true of players on playoff teams.
Many of the players attend because Hawaii is a nice venue and the family wants to go to the beach in Feb. (particularly true for players on teams that play in the snow). While Miami is a nice place to head to in Feb. Other SB venues are not. Hold the pro-bowl in Indy or Detriot and I think you will see plenty of players skipping the pro-bowl and just take their family on vaction in Hawaii instead.