Yes, it seems strange, but Civ 5 manages to extend gameplay beyond 2050 just fine imo, I don't see why it's not left as an option in the core game. Civ 5 has an option to auto-end the game at 2050 - but if I'm in the middle of an important war then, or I am just about to win some victory type or something else I enjoyed being in the middle of, ending the game because of some arbitrary day occuring seems incredibly stupid.