Personally, I don't think it has anything to do with durability. Sure... UL equipment is not as durable as more robust / heavier items, but you get used to certain limitations and adjust accordingly.
Education is probably the key between us and the masses. Most of us didn't start off as UL backpackers, including myself. I just didn't know these products existed. If I was comfortable carrying 50 lb packs, I would probably still be doing so. However, I wasn't. My discomfort led me to find a better way.
For others, it's personal choice. Some like the idea of having backups, and more durable products, and creature comforts. They deal with the weight for the idea they are more prepared, and comfortable at the end of a long day of hiking. Personally, I would rather be more comfortable hiking. The key for me is to find a gear list, a particular weight, that is comfortable to me while hiking and that makes me comfortable while at camp. It's taken a while... but i've finally gotten to a point where i'm happy.
Lastly, cost. There are few of us, and many of them. There are more supplies making the products that they buy. Supply and demand. More competition leads to lower prices. We are a small group with limited producers of the products we desire. Thank God for people like Ron (MLD), Rand, Joe, Tim, Ben, Glen and Grant, Ron (SMD) and Tom who are dedicated to our practice and needs. Without them, we wouldn't be able to do a lot of the things we do. Not with my sewing skills that is. We pay the price that is currently required to produce such high quality products, and I'm happy to do so and will continue to do so.
I will never say my way is better than your way or another person's way... I just do what makes me happy. I think that's what everyone should do.