The camper was originally designed for the old 3-jack system, so it most likely did not have adequate structure for the four corner jacks.
The 3-jack system went out of style in the 80's or early 90's so any camper that came with it has to be at least 30 years old, and won't be in the best of shape structurally, either.
Worst case, it was lowering single jacks 2" that ultimately caused the failure. On my camper, 10 cranks is about all I can lower a single jack working alone. 2" would have the jack foot completely off the ground on my camper.