my all time fav jazz piece is "strangers on the shore" by acker bilk.its been used in loads of tv ads through the years.why is jazz used so much in tv ads.?

Same reason electronic music is used in TV ads a lot. Lots of stuff w/out vocals and the good stuff can catch your ear.

maybe it's royalty free

And what about jazz music(and classical also) in cartoons?

music made for coinciding with anime tions and movies like scoring is crazy because ita suposed to convey raw emotions, feelings, moods, and such