Because they take everything literally.
What's the difference between an Englishman, an Irishman, and a Scotsman?
The Englishman lives in a house, the Irishman lives in a flat, and the Scotsman lives in a bothy.
Why did the Scotsman wear two kilts?
Just in case he got a wee bit chilly.
What's the difference between an Englishman, an Irishman, and a Scotsman?
The Englishman drinks tea, the Irishman drinks whiskey, and the Scotsman drinks Irn-Bru.