Like others, I have no real information, but some further speculation: Is it not likely that a fiddle is more easily adapted to the solitary nature of frontier lifestyle? What I mean is that the frontier was generally a very lonely place, with homesteads being fairly isolated. In that situation, I can see keeping a fiddle around to amuse oneself and one's family in the evening or during the long winter months, with the very occasional community even thrown in. Maintaining a set of pipes (of whatever type) would seem to be an extravagence in a hardscrabble life. (Perhaps this is just another way of asking if the "critical mass" of pipers wasn't sufficient to offer a source of supplies & repairs.)