I'm gonna guess that they don't have the RAM budget to spare to load all 32 teams' helmet assets (raster / normals / etc.) into memory at once. If that's true, something in-game would have to get cut to get proper Pro Bowl helmets in, be it an across-the-board texture fidelity decrease, fewer triangles / textures for stadiums, less audio / commentary, or what have you. Pick your poison.