Whenever they make a new installment to a title and change core fundamental functions, their excuse is always something along the lines of "it didn't make sense before, so we're changing it" or "we felt it didn't fit with the whole idea, so we're changing it" or "we didn't think it was much fun so we're changing it" etc.
Basically what they're implying is that the the previous game mechanics was crap, so they're gonna change it. Well that makes the consumer feel better...knowing that the game they played the whole time was actually sub par in comparison. When they do come out with EU 5, HOI 5, Victoria 4 or whatever, i wouldn't be surprised if they say the game mechanics of EU4, HOI5 didn't make any sense once again.
Thats generally true, we try and iterate and make every game better. With each version we generally get closer to where we want to be. Generally what happens is we make expansions, or DLC with the new model for as long as the basic mechanics dont frustrate us too much (they can not really change except for a sequel).
There is also the fact that some games, particularly HOI have had different lead designers and ended up quite different because each person is doing the game they want to do. Just updating the game for better graphics is boring and pointless. I also think this leads to a fresh experience - Journalists often ask me why people would want to play through WW2 again after they did so in HOI, HOI2 and HOI3, but those games are all very different experiences, and HOI4 will be too. There was a lot of "crap" and "sub par" mechanics in previous games, and even the stuff that was working well can be improved. Is all the new mechanic guaranteed to be better? Perhaps not, I prefer to try some risks to come up with innovative stuff rather than conservative and safe. Will all HOI players love it? Absolutely not, there are many different HOI players and they all like different aspects of the games (just look at the debates on number of provinces between HOI2 and HOI3 fans), but I hope the vast majority of people will agree that its a big step forward. All we can do is listen to players, and do the changes we ourselves want to see and iterate on that, making each game and expansion an improvement.
also secret masters points are all valid