Two types of earth fighters existed in 2261: Thunderbolts, for attacks into atmosphere and Star Furies for space combat. Star furies were the better for the latter: better than Thunderbolts, which left the pilot less freely oriented in space (because the Thunderbolt design featured sitting pilots).
Why would the design change? Simply saying that it would is futile. It is like saying that planes of the future will not feature two wings, because planes of the present feature two wings, and in the future they must feature a different number, by definition.