at the same time, things are changed like adding RPG elements in order to enrich the game experience.. no one adds elements they think are going to detract from the experience on purpose. sometimes tehre are growing pains along the way.
Well, obviously. Changes can be made to try and improve it, which may or may not work out. Mass appeal is not done to intentionally ruin a game, but it IS done to intentionally make a product more like Game B than Game A, because B sells better. Fans get so angry because the minority gets shafted, every single time. Companies like the largest demographic the best, but they still want money from the smaller ones, and will often make a new franchise that seems be catering to them, then makes a sequel that goes right back to the masses so they can get both the majority cash and some new brand loyalty cash. People whose preferences are in the majority rarely see a problem, because they're always catered to and to them the games just improve. Others are pissed off by constant baiting and disappointment.
There's also the fact that in its earlier days, gaming was a niche thing. There was barely any "mainstream" to aim for, and you could afford to make a game that was awesome to a few people and not appealing to many others, because "a few" was already the expected player base. Between the industry's current popularity and costs now in the millions of dollars, they won't take that risk. Products in any medium being diluted toward mass appeal is inevitable, but gets especially annoying for people who remember an alternative.