The "But wait, there's more!" device predates infomercials. It goes at least as far back as the "Atlantic city boardwalk pitch" from the early 20th century:
https://en.wikipedia.org/wiki/K-tel
> K-tel was founded by Philip Kives,[4] a demonstration salesman from Oungre, Saskatchewan.[5][6] Kives had worked at a number of jobs as a young man, including selling cookware door-to-door and in a department store, and as a pitch-man on the Boardwalk in Atlantic City.
