I'm not sure if the historic background is known, but we could look for a time when new castles were being built in England (which would imply a time of prosperity and upward mobility) and masons were being brought in from the Low Countries (one theory is that "Lamkin" is a diminutive of the Flemish name Lambert). Either it was early enough that castle-building expertise was unavailable in Britain, or so many castles were being built that the demand was greater than the local workers could supply. This is all, of course, pure speculation.