I've owned multiple F150's and Expeditions over the years; and, I've replaced a lot of front wheel bearings. Thoughts on Front Wheel Bearings:
All other things being equal, the larger diameter the wheels, the shorter the wheel bearing life. This is a simple moment issue. It's the same reason that the larger diameter wheels translate into more stable cornering: more lateral G's are put to the bearing rather than being absorbed via sidewall roll on tires with taller sidewalls.
All other things being equal, trucks/expy's with Aluminum Knuckles go through bearings faster. I believe that is due to increased stress due to thermal loads as the bearings and knuckles expand and contract differently under thermal load. The Aluminum actually increases compressive stresses on the bearing outer diameter. Add a corrosive rustbelt environment to the dissimilar metal problem and galvanic corrosion will accelerate the failure much faster because corrosion on both parts adds pressure to the bearing.
Finally, as an engineer who has been involved in specing and procuring bearings for production applications over the years. It has become increasingly difficult to procure high quality bearings due to a lack of capacity for higher quality bearings and increased global capacity of lower quality bearings. I've also had to buy several sets of front wheel bearings for my 2007 F150 over the years and I've found premium Motorcraft and Timken bearings last fewer and fewer miles.
This is one of the reasons I went with the FX4 on my 20 Expedition with the 18" wheels. I know it doesn't corner as well; but, I get less mud inside the wheels off road, and I'm hoping to extend my wheel bearing life a little bit. But, I do wish they had put a steel knuckle and aluminum control arms on the 4th generation instead of the opposite.
The good news is, it's a pretty easy repair. I can change a set out in under an hour without rushing.