"What ever we me think about folk / traditional / art / composed songs isn't it the case that when it comes to instruments the divide barely exists. I guess pumped or blown bagpipes are essentially "folk" plenty of other instruments exist in both or all camps of performance?"
I wouldn't have a clue - not knowing anything about the culture and history of music, it's an interesting thought. But venturing a few guesses, I'd think that there may be pragmatic elements, which while not strictly 'dividing' the instruments of the lower classes from the upper, might have shaped their predominance somewhat.
I'd guess that 'folk' may have generally had instruments which were easily portable, could be constructed from readily available materials, not requiring a high degree of musical support in terms of fellow instruments (bagpipes have their own accompaniement in the form of a drone don't they?), err not too big and bulky etc...?