I have the feeling God had the Japanese invent the Kotatsu for the same reason he gave the Scots Scotch. That is, simply, to keep them from taking over the world (though nothing about them trying...)
Funny verbal fact: Scotch is a capitonym (a word that has different meanings based on whether or not it is capitalisized). When Scotch is capitalized, it can refer to the people group or to the drink. When it is not capitalized, it is a verb meaning "to destroy".
Thus one may say with little exaggeration that God created Scotch to scotch the Scotch.