Presumably because it would add around £1000 to £1500 to the cost and you have only really needed them since Al-Ko started using their effective but very awkward to fit wheel lock.
As well is two words!
How does a sage know everything about everything? or does he? or does he just think he does?
Remember, if you buy something you bought it, not brought it.
Surely the people who want them are unable, either because of age, physical limitations or inability, to reverse a caravan of any description. Cost is the obvious answer, but
maybe there would be a market for it.