My take on this is, analog TV been around for a loooong time and for a loooong time the only way to hookup anything external to it is via the RF, so they made it inexpensive for ppl to do it?
Nowadays, when ppl hookup external source to TV, we don't think of the antenna, because there are other more direct options. If your mother bought hers right at that time when digital TVs didn't have HDMI/Component/Composite, ooops. What am saying is, am guessing they don't make many of those ATSC modulators to bring the $$ down and market to street Joe consumers.