Exactly correct. I was told by a tire store locally i know and trust that the vehicle manufacturers put out for bids to tire oems and then go with the winning bid. The tire oem then makes thousands of tires for the vehicle oem under the bid\order. As such, to keep costs down they don't use the same quality rubber as they do in their regular/non bid tires.
Again, this is what i was told and it makes sense. I like Bridgestone / Firestone and specifically the transforce. I put a set on a 2000 expedition and they are the oem on my 17 ram. I like them. To each their own though. Bridgestone potenza is an excellent car tire also. Good luck