That's due to the nature of economic engine games. When you're just starting out, it's an uphill battle where every decision matters a lot. When you get past a certain point, you enter what my friend and I like to call the "mop-up phase." This is the situation where your opponents are extremely far behind, with no hope of catching up, and your decisions matter very little. Not only do you have to make a lot of mistakes to even come close to falling behind but your good decisions are inconsequential as well.

Game designers have thought long and hard about this problem over the entire history of the genre. There have been numerous attempts at putting in mechanisms to slow down a player with a large empire but they often just make the game more tedious. I think this is the wrong approach. Once you reach an overwhelming advantage the game should allow you to close it out easily.

I think of chess at a high level. If no player ever resigned, instead forcing their opponents to perform extremely long, drawn-out checkmate sequences in theoretical win positions, people would hate it. Just resign so we can move on to the next game!