Spot on, Abby -
There are, indeed, many different Scots languages in Scotland! Our own Robert Burns managed to incorporate bits of many of them in his songs (lookin tae maximise his mercat, nae doot); and there are lots of examples of 'traditional' source singers (Stewarts etc.) swinging between various different Scots variants of the same words (and even English) in the same song! So - lots of reasons and motives.