Crystal Dynamics is pitching this as a solution to the [made up] problem that people level too fast and are having trouble handling all the skill points the game throws at you.
Having played quite a bit of the game I can tell you that this makes no sense. Leveling isn't particularly fast, especially if you switch characters a bunch, and the skills are all super easy to understand and integrate. I'd say it actually takes too long to get enough skill points to make characters somewhat fun to play.
Furthermore it only affects characters from level 25 onward, when you already have a good handle on the character and their various skills. It's just a transparent lie.
They also encourage people to get to level 50 before the relaunch if they want, which...
Anyway my only two thoughts about the actual reason would be:
1) They think that they can get people to stick with the game longer if they draw out the grind, which is possible I guess, though it won't make the game 'better' in any way since there still isn't enough to do to justify that grind.
2) They are going FTP and are going to sell XP boosters and this is laying the groundwork for that.
I think 2 is the most probable explanation. Given where this game is right now FTP makes a lot of sense. First you get the last batch of premium buyers with the next gen version and then some time in the summer you flip the FTP switch (long enough that the previous buyers don't burn down your headquarters) and start doing more FTP stuff rather than the current "just cosmetic" version of the stuff.
Will it work? I think FTP is pretty much the only move left at this point. The license will make people curious and you might get enough of a player base to juice some more cash from the game, as well as maybe getting that critical mass of players that you don't have currently. I just wish they weren't screwing up the XP curve to do it, if that's the plan.