The villain in this piece may well be the melodeon(or diatonic button accordion), which swept through the world carrying all before it in the late 1800's. While fiddles played easiest in D, G and A, at least with a bit of practise you can play in other keys as well. But once someone in the pub turns up with a one row, or two row diatonic box, you're scuppered. Coupled with the simple whistles and flutes, with the 6=holes closed note as a D, and the influence to stick to a handful of keys is very powerful. Examine a few fiddlers tunebooks of 1800-1850( a fair few flat key tunes included) with fiddlers' books today(hardly any flat keys), and the point becomes obvious.