While most major manufacturers offer lights that run with AA's, Their flagship line of lights usually run on 18650's as this has the best power/size ratio for their powerful lights.
Though some manufacturers will make lights such as the Fenix TK41, the Olight Baton S65 and S35, the Fenix LD40, the Jetbeam PA40, (I just mentioned the bigger ones), they know most clients would opt for the smaller and more powerful light.
Case in point, the TK41, runs off 8 AA's compared to something similar in performance that runs of 2x18650's, the latter would be more convenient to lug around due to its smaller size.
AA'S are a good light to have but the flexibility of having more output in a smaller package is what sells those lights more than the traditional AA configuration lights.
I do not hate on the AA lights, in fact i have several, but these can also be upgraded to run off 14500's for better output!