Why no shortwave band on radios?

mapj1:

And good quality SW reception requires more careful receiver design, both as tuning needs to be multi-octave, an a choice of IF frequency that is OK at MW may lead to spurious responses and lack of selectivity at the 20-30MHz end, and as the dynamic range of adjacent signals can be very high. It is not uncommon to want to extract a signal of a few hundred nanovolts RMS from under the skirts of an adjacent unwanted one at tens of millivolts RMS that may be 10-20kHz offset. For these reasons the common (=cheap) solution on a MW/LW set of  single tuned circuit prior to an unbalanced 1 transistor self oscillating mixer is not likely to be adequate, so attempts to extend an existing LW/MW design cheaply are usually a disaster.

It's a fiddle but I have seen it done. RF transistors almost always need to be replaced by those which operate at a higher frequency. Parasitics can be problematic because the PCB is designed to operate at a lower frequency. The converted radio is usually intended to operate around the frequency of a particular radio station the user is interested in rather than attempting to cover the entire SW band. LW / MW radios were often converted into SW radios in countries where SW radios were difficult to obtain.