Why was the Spitfire's elliptical wing almost uncopied by other aircraft of World War 2? The Spitfire was one of the most successful designs of its day, with flying qualities of a similar standard to the other best designs of the era. In its decade of production from 1936 it grew bigger, stronger and faster.

Yet there seems to be almost no appetite from any of the major aircraft-manufacturing powers to emulate its most iconic feature. In fact, there is only one mass-produced aircraft of that time with an elliptical wing, the American P-47 Thunderbolt. Nothing German or Japanese, and nothing more from the British either.

In a period where every manufacturer was trying to gain every last bit of advantage, it seems odd that a prime design feature attracted so little appetite to copy.

There are good explanations here on the aerodynamics or performance of the elliptical wing. Why is it so rare when it demonstrably works so well?



Source
Interestingly, I couldn't find an answer to this question on the website, but I've found an answer of Peter Kämpf on Quora. He brings forth the same arguments I wanted to mention, so I'll repeat them here.

Elliptical wings are very good - aerodynamically. If you want to minimize induced drag for a given lift requirement, you end up with an elliptical wing. 

But a plane is not only aerodynamics. 
You also have to consider:


Weight, an elliptical wing is not structurally efficient, and will lead to a higher weight, which leads to higher lift requirements which will lead to more induced drag, even with a very efficient wing.
Controllability, where and how the wing stalls determines if you're able to recover from a stall. Elliptical wings stall tip first, leading to bad stall behavior.
Manufacturability, a fully elliptical wing is very hard to make, with its double curves. This will make the wing more expensive.


If you include these factors, you'll see that you'll end up with a compromise. If you use wing taper (which is somewhat close to the aerodynamic optimal shape) but much easier to make and much lighter you'll see that you'll end up with a better design overall.

An analysis of how the design of a wing changes if you include the structural requirements was done by Jones and can be found here.