I too have seen several Youtube videos of broken springs, one on a 16 ft cargo trailer being used as a camper, another on a 20 ft or so travel trailer, and another on a larger trailer, a fifth wheel if I recall. In all cases the spring that broke was the main leaf, out in the area where it is unsupported by the other spring leaves. I highly suspect the problem is cheap imported products, used by Dexter and Lippert and others. This may be the reason that in days gone by, it was unusual to see a broken spring, as the springs 30 or 40 years ago were US made and from US steel.
Gonagain has broken spring on their cargo trailer conversion.Grand Adventure breaks a leaf spring enroute to the Canyon of the Ancientshttps://www.youtube.com/results?search_query=Broken+leaf+spring+rvUS trailer manufacturers seem to be unwilling to install a quality suspension system on their products, as they regard the whole trailer as disposable and not worth the extra expense of a quality suspension.
I wished I had a trailer with a suspension such as the Australian made Cruisemaster.com.au or the alko.com.au suspensions.
Charles