I think one of the biggest factors is the rebirth of the "super-light" and "ultralight" travel trailer (and toy hauler).
When they shed weight without increasing the price, manufacturers sacrifice quality and strength of materials.
That and, of course, the almighty "race to the bottom". The race to have the cheapest price point on the market means cutting ALL of the corners.
Back to light weight...
You can compare similar trailers from the same manufacturer, one being of 'standard' construction and the other a 'light weight'. The light weight model will nearly always feel cheaper, more fragile, and poorly built.
One of many examples of why no one in my family will touch anything built within the last 15 years:
Five(?) years ago, one of my brothers bought a 28-foot fifth wheel trailer for camping and hunting, when he was presented with a good deal from family. (Essentially, a "take over our payments" situation.)
It was nearly new and in good condition.
He used it for one season and traded it on a comparable and similar age bumper pull trailer from a different manufacturer.
That one lasted one season, as well.
He sold it and went to something else - which I'll mention later.
The problems were build quality, material quality, and lack of insulation. ...As both trailers were "ultralight" models.
Propane burn to heat those trailers was substantial. And the walls had condensation issues.
Every time they used one of the trailers, something broke - not just appliances failing, drawer pulls coming off, or electrical issues; but the actual structure. Someone would bump into a wall, and the paneling would crack. They went to convert the couch to a bed for my son once, and the entire cabinet face for the storage under the couch pulled off. The kitchen sink plumbing leaked. All of the blinds broke within a matter of months. The electric-only slideouts (no manual crank on the light weights!) failed to retract several times. The propane piping developed several leaks. The propane regulator failed. The stereo system never worked properly. And on, and on.
The kicker, the final straw, was in the 'bunkhouse'. The second trailer was a variation of a toy hauler trailer where the rear portion of the trailer had five fixed bunks and a side door, instead of fold down bunks and a rear door for ATVs. During a wind storm on a deer hunt when they had already had one problem after the other with that trailer, one of the bunks separated itself from the wall. The bunk and its occupant were dropped onto the person sleeping below.
My brother's solution, after selling the trailer?
He went back in time: He bought second-hand, but new, the largest available
Cabela's Alaknak tent, a wood stove, half a dozen cots, and a 5x10' cargo trailer.
"I can sew if it tears. I can feed a fire if it's cold. And I can haul everything around in a much smaller and lighter package..."