I too have this "problem", but with pretty much all sandbox games, strategy, simulation, builders, RPG...
When you get to the point where you can no more lose, are the strongest in every aspect of the game, one shot everything, etc, there is no real point to go any further...
The initial struggle is fun, the rise in power is fun, the top dog status is fun for a while, but after that, the "hey look at me how super strong i am and how even more super strong i will be soon" is not, no point to continue...
What for ? you wont really impress the AIs and noone but you care about your game.
I still make a point to finish at least one time, just to see the end, but thats it.
When you get to the point where you can no more lose, are the strongest in every aspect of the game, one shot everything, etc, there is no real point to go any further...
The initial struggle is fun, the rise in power is fun, the top dog status is fun for a while, but after that, the "hey look at me how super strong i am and how even more super strong i will be soon" is not, no point to continue...
What for ? you wont really impress the AIs and noone but you care about your game.
I still make a point to finish at least one time, just to see the end, but thats it.