"Clan Buchanan has occupied the lands surrounding the shores of Loch Lomond since 1225 as a result of a grant by the Earl of Lennox to Sir Absalon of Buchanan in which he is referred to as 'clericus meus', meaning 'my clergyman'. Towards the middle of the 13th century Gilbert seneschal to the Earl of Lennox obtained part of the lands of Buchanan in Stirlingshire and took his surname from the lands called Buchanan.[10]"
Maybe this is why.And for good reason....Still searching.