"I wonder w how many people go on to get a lasting interest in folk music through encountering it in advertising jingles"

Probably not many but, bearing in mind that acoustic music of any kind - let alone folk music featuring fiddles, accordions or natural voices - is an entirely unfamiliar sound to a lot of the population, anything that primes them for that kind of sound is going to make them a tiny bit more likely to respond positively if they ever hear actual folk music at some point in the future. I didn't much enjoy the folk music I learned at primary school, but I do think it at least familiarised me with the sound of the stuff.

"Bonny Bunch of Cadbury's Roses"

Good one, Al!