that’s because the trucks you listed are HALF ton trucks by their model number.
F150/1500 is half, F250/2500 is 3/4 and F350/3500 is one ton.. GM tossed in the HD’s to mess with your head.
In the old days 1500 = 1,500 pounds load in the bed capacity i.e. 3/4 ton. In Ford they dropped the trailing 0, F-150. A 2500 = 2,500 load and 3500 is 3,500 pound load. I do not think that that has changed. I had an old F-100 and it was rated at 1/2 ton but it could carry more than that.