[JRTJH]

This has happened a couple of times in previous years and in different brands. Just one "potential way it got past":
Lippert built the chassis "per Lippert/Keystone specs"
RVIA changed the tire capacity to recommend a load capacity increase
Keystone (with/without Lippert coordination) increases the size of the tires
Keystone ships trailers to dealerships empty, there's no "tire contact problems"
Owners load trailers to GVW max, there's "one outrigger" above a tire that might rub if towed over rough roads or that doesn't provide for sufficient tire travel clearance.

Should it happen? Nope,
Does it happen? Yup, to all manufacturers, especially with changes in spec requirements after design, during manufacture and delivery.

Another probability: Keystone changed from MorRyde suspension to Lippert's suspension (Road Ranger, I think it's called) which has more suspension travel at the equalizer. Lippert says, it's cheaper and better, Keystone installs it, finds the increased travel doesn't really save money, it costs a recall.

I don't have any specifics on what really happened, but I can see several ways that it slipped past everyone. More a case of "sales promises" than "engineering confirmation".... Sort of like the customer hears: Sure, your truck will tow anything on the lot".... Manufacturers get "sucked into that sales gimmick" too....