Between my parents and my family we have had 7 RVs since the 70's. In order to save weight the manufacturers use build techniques which are not as beefy as sticks and bricks houses. They do have to take into consideration the travel aspects of RVs and make them strong enough to survive various road conditions and weather.
Unfortunately as a brand or model becomes popular, the assembly quality may suffer in order to keep up with demand. Our first 5th wheel was one of the first on the market with two slide outs with one of the slides being 14 feet long and 4 feet deep (super slide). This model became so popular the factory added a third shift to try to keep up with demand. So you can imagine a worker on the 2nd shift might be installing a sink and end of shift comes with the task not complete. The 3rd shift may not be aware the sink install is incomplete and the trailer ends up being shipped with loose connections. Our 1994 5th wheel had over 25 problems, most were cosmetic with only a few mechanical issues.
Lack of quality is not just an RV industry issue...Our friend who bought a new house recently had over 300 problems identified during their final walk through, it was a 5000 sq ft house. Another friend had his oil change at one of the quick oil change places and drove off he got a few miles away and his engine seized up. They hadn't put the oil filter on.