I don't know where you are, but of the various places I've lived in the US BabaG isn't common at all on store shelves. And of the 3, tahini sauce would be a VEEEEERY distant 3rd in terms of popularity, so that's the simple answer. Its not on shelves because there's no real demand. And additional speculation is that hummus and BabaG are significantly more work than a tahini sauce, further reducing demand.
SF Bay Area, so I guess you could say we are a "food forward" kind of place. If you walk into Whole Foods or The Berkeley Bowl or Rainbow Cooperative in SF you will be amazed at how many brands of Hummus and even Baba ganoush you'll find.
Decent baba is hard to find at regular grocery stores, which makes nonsense because it’s far superior to hummus. They’ll have 40 varieties of hummus, including weird stuff like chocolate, but no baba.