It has always been that way with Total War games, in fact it happens in most games. Technology changes, new things become possible, would you rather they just stuck with the same old tech so that we could reuse old files in new games? Doesn't that pretty much undermine the whole point of making a new game in the first place?
Modders have always had to start over when a new game comes out, its just a part of modding in general not some great injustice.