What? Everyone always complained about that because maps were either built first with Conquest in mind or with Rush in mind and the other modes sucked on them. The Battlefield community has been asking DICE to make specialized maps for modes for years.
I don't think it's a good thing if it means only 4 maps for the main game modes tho. And besides you get 4 completely different modes that all play in the same 4 "big" maps anyways so they aren't exactly doing specific maps for specific modes. If there was Rush in this game, it would still play in one of the big maps so that problem is not really addressed here with what they did with this game.
They could've just easily cut out 10 small parts of 10 big maps for the smaller modes like TDM if they had made 10 big maps. I don't see anything special in the current small maps that could not have easily been a cut out of a larger Conquest style map, Just like they do in Battlefield.
This is all just an excuse for them, the fact is they only released the small number of maps they did because of the 18 months development schedule they had to follow. I also think that insanely short development time is the reason they didn't include Conquest Large even tho the old battlefront games had 64 player Conquest. Conquest maps would've probably been a lot more work to make than the current very linear and much smaller "big" maps we get now.