That's legalese for their lawyers insisting they make no claims for anything to minimize their liability. They are definitely strong enough. 20 years ago I bought an Olympic bumper with an integrated receiver hitch and it was rated for towing when I bought it. Years later I looked at it to include it in a recommendation and they no longer rate it for towing even though no changes were made.
I have run the Dirtworx bumper for the last 15 years or so and it tows my pop-up tent trailer nearly everywhere I go and it is obvious that it is WAY more than strong enough for the job.
It would be very difficult nowadays to find a bumper that specifically says it is rated for towing. Blame the lawyers and the inability of small manufacturers to be able to afford to buy enough liability insurance to cover every possible situation with all their products. People are now lawsuit-happy even when it's their fault. "Drunk and killed a bicyclist but he's suing the car manufacturer for making it too easy for a drunk driver to start the engine." Right.
This is the trailer I've towed behind two different TJs on bumpers "not rated" to tow. Give me a break.
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