Or it's just that you are always godly powerful by 1700 that continuing the game becomes a tedious proposition.Just hopping in one moment to point out that I usually poke around quite a bit, before starting a certain campaign. I might start six-seven games before settling on one. And yes, removing later start dates would impoverish the game greatly - I played elsewhen, from time to time.
But the main problem - and one very tightly connected to the "no games beyond 1600" one - is that EU4 has no endgame. No, revolutions are not enough. Wars are wars, and one more war does nothing to shake the game. What the game needs is industrialization, the development of more complex diplomacy, the Scientific Revolution and the Enlightenment. Something that makes you see that you are travelling to somewhere else entirely, enough to make you want to play there - either getting there or starting there. Basing your choice on unweighted data, while the last part of the game has no gameplay to speak of, makes little sense.
I agree that bookmarks should not be removed. I play them from time to time and there should be more achievements for them.