For hundreds of years and thousands of centuries, UPS has had drop-frame trailers, which would not have worked with higher pintle hooks. Not too long ago, the door even went clear down to, almost, the ground, near the hook (remember that, those of you who have been loaders, unloaders or drivers? Boy, if that thing was in a door, try opening or closing that suspended hanging upside down!)
All of the dollies are still designed that way, to accomidate the lower hook. You can't use one of our dollies with a regular freight trailer. They would have to start a new line of dollies to go with a higher pintle hook. Think of the unbalances we would have then!
Think of what we've had even WITH the same dollies. When I started, we had 24' trailers, some with hooks on back, some not. If you had 2 24's, one 50% and the other 100%, it didn't matter how they were hooked if the 100% didn't have a hook. It always had to go on back. Good planning? Yes! Good driving? NO!
Then we got 26'. More imbalance. Sometimes 26's had to be put on back of 24's. Then 28's. Same thing. Then those confounded lift-off, container pieces o crap! Nothing was EVER right about those! Still ain't! The king-pin is closer to the cab, they ride like glunk, catch the wind more than anything I've ever pulled, doors won't close, etc.
Now the new flat-floors. More imbalance. Flat on front? Drop on back? Container on front, back?
My opinion? We'd have so much more imbalance if we'd convert entirely to freight type dollies. We'd have some centers with regular dollies and freight trailers, some centers with freight dollies and drop trailers, etc. Sure, this is blowing it up a little bit, but those of you that are feeder drivers already know what a circle-j### it can be already trying to balance 2 or 3 trailers.
Maybe some day it will happen but I hope to be gone by then.
also has a lot to do with trailer specs and the fact that ups has 99% silver eagle dollies just for low p/hook's as upsgf has fruhf and strck dollies that have dolly roll up legs which were common dollies for 90% of LTL carries in the 1980's and 90's they could just roll them to the back of units and roll the leg up were now they have new silver eagles they have to pick them up to hook, but on the safety side the s/eagle's have a great balance and anti-roll feature with the spring over frame feature.