If you want to measure distance travelled over the earth you want nms since the earth is a sphere and you don’t want your route length to be longer when you’re at higher altitudes

If you’re measuring distance in nms you want knots as they’re nms/hour

We use kms for other things though- like weather minima, runway length - things on (or close to) the surface. Eg I need either 5km or 8km forward visibility to enter some controlled airspace.

Ft for height is less functionally defined though- that’s just the way it is because it’s the way it’s always been. Not much gain in changing it though

Uh huh... feet is more useful for aviation than meters. 1,000ft is a comfortable vertical separation between planes and it's a nice round number instead of ~300m.

As for nautical miles and knots, one nautical mile is equal to one minute of latitude making for easier navigation when you're traveling over significant distances of the planet.

I'd hardly call it stuck in the past but rather the right units for the application at hand.