The difference in motivation in getting the Frostbite 3 engine running on the Wii U vs the 360/PS3 is the installed userbase. Its near impossible to create a AAA games these days for a new console without taking massive losses, so a buffer period is now needed where they release on both current and next gen consoles. EA is looking at the Wii U's userbase, and and the current sales pace, and decided that it wouldnt be profitable to support the Wii U. They most likely feel that they tested the waters with Mass Effect 3, Madden 13, FIFA 13, and Need For Speed Most Wanted, and none of their games have sold very well. Sales history on Nintendo consoles for EA has typically been far worse than on competing consoles. So combine this with some salty feelings about a failed Origin deal, a rocky past history, and we are finnally to the breaking point for the Nintendo and EA relationship.
EA wasnt planning on supporting the Wii either until it was outselling the competition by significant margins. If sales pick up for the Wii U, EA will be back to try and get a piece of the pie. They may be trying to throw their weight around to score a better deal on royalty fee's that it pays Nintendo for each copy of its games sold, but Nintendo may not be willing to budge on that.
Either way, it has nothing to do with the hardware not being capable enough, but that EA doesnt want to invest the money to optimize the engine for a console that they dont see as a viable platform for thier games to sell well.