At the present time I suspect the E-Boost has lot to do with it. Good low end torque. But I believe that Ford F-150 simply outsell the competition so you will naturally get more Ford owners on the board.
Despite claims to the contrary, for the average Joe or Josephine any truck that is suitable for the load will do the job regardless of brand.
My F-150 4x4 is rated 1411 lbs. Max cargo; so with the DW, dog, stuff and tongue weight of our 5000 lb. TT when loaded, it is at its cargo limit. But, since most people tow less than two month out of the year and they use the TV for regular day to day driving, the F-150’s 18 to 20 mpg on the highway, lower cost of maintenance than bigger trucks and diesels, add to its appeal.
In answer to your question, also keep in mind that a fair amount of the ½ ton TV are probably towing RV’s that or at or over the recommended limit but the performance is suitable to their owners. A product that meets the owner’s needs, at a cost they can afford, will always sell well.