The construct of what we call 12 bar blues predates the concept of blues, and the format of AABA /12 was very popular in music hall, not to mention traditional ballads, as pointed out by many, including Vaughan Williams.

Accordingly, I used to enjoy singing St James Infirmary Blues to the tune of Harry Champion's When Father Papered the Parlour. The other way round gets a giggle occasionally too.

I suppose it was the prominent sound that a "blues" scale gives to the tempering of a guitar pitch that kicked it all off, but the format over twelve bars is one of music in general, not one genre, albeit a genre that grabbed it and made it its own.