From what I understand, it's not so much a case of deliberately doing away with it, as it is the engine from Empire onwards not being designed with modding in mind, thus making it MUCH harder to do. They've apparently had talks with modders recently though, and are trying to make the Rome II engine a bit more modding friendly.
---------- Post added 2013-06-14 at 01:46 PM ----------
Hi. I'm someone involved in the games industry. Did you know there's a period of several months inbetween when the game is completed and when it's released in which bug testing and fixing is done by the programmers and testers. During this time the artists and designers have nothing to do; in the past they would just be pushed onto another project, but instead now they start making extras for the game beyond the original scope of the budget. This is your DLC.
Point of fact, the game is complete, the DLC is extra. You want to get the extra, you pay for the extra work they put in.