If an elliptically-shaped aerofoil gives the optimum lift distribution, why aren't propeller blades designed around this ideal?
If an elliptically-shaped aerofoil gives the optimum lift distribution …

I interpret this as an elliptically shaped wing, because only then the question makes sense.
Propellers are similar, but not identical to wings.

Dynamic pressure varies along blade span. The outer sections needs less chord for the same lift compared to inner sections.
Propeller blades operate at the start of a helical wake, so induced speeds are different than those on straight wings.

What is required is not an elliptic lift distribution, but minimum induced losses. Albert Betz showed in 1919 that the optimum induced speed is constant over the propeller disk, just like downwash is ideally constant over span for minimum induced losses. Based on this, Larrabee found an efficient computation method and practical propellers have to find a compromise between theory and practical constraints. The most important are

Compressibility effects near the tips (which force thinner airfoil and lower lift coefficients than what the ideal prescribes). An extreme case is the Junkers VS-9 propeller used on the Ta-152.
Structural limits at the root (which force the use of much thicker airfoils).

Betz' theory is meant for lightly loaded props. Once disk loading goes up and the propeller diameter cannot grow proportionally, propeller chord and blade count grows and the main concern shifts to converting all available power to thrust. Concerning fancy blade shapes: They have more to do with marketing or unscientific voodoo beliefs by some hobbyists. Generally, a straight shape works best.