Diminishing returns....
There is only so much money and manpower that could make a game fun. Look at Duke Nukem Forever, FFXV, BotW, Last Guardian, or any other game with a very long development cycle.... It's not the length of development which makes those games fun or not fun.
If you don't nail the concept early on and stay true to the vision, then more money and time would not make a game a blockbuster. Adding more, and more, and more to a game for years just to increase the spectacle doesn't really change or enhance the product like you think it would. Yes, it can add polish, but the team has to decide very early on what the game will look like and commit to it. There's only so many unique things you can do with a core concept such that 7 years makes sense to keep adding stuff.
There's also no reason to turn 30 hour games into 200 hour games. Chances are, the first 30 hours will be far more fun than the last 170. And if you really inject enough variety into your game such that each 50 hour increment in a 200 hour epic is truly distinct and different, then it may be best to divide up those chapters into several games anyway.