My theory is that the gallery is an EA online service, so to make that service available through PSN or XBox Live would be quite difficult and tedious as certain terms/conditions or agreements might be difficult to compensate for. Not sure if you heard but PlayStation is quite restrictive with their online services when it comes to opening up to other services. An example, the minecraft better together update won’t be available on Play Station consoles, so while PC, Mac, Nintendo, and Microsoft minecraft players will all be able to play cross platform together, PlayStation users will be left out.