The larger national brands tend to have longer supply chains (suppliers between the manufacturer and the consumer), the largest "markup" at every step, and most lean more towards selling "stories" than towards selling value. They often work very closely with the larger retail outlets and chain stores and have large marketing departments that help determine which stories will sell the best. Each series of complaints about poor quality of construction is usually followed by a new model with a new story (or name) attached that somehow represents an improvement even though it is a virtual duplicate of similar mattresses that have been sold for many years. The outlets that sell them are usually well trained in how to convince consumers that the "new models" effectively deal with the complaints and that "last years models" are now "on sale" even though you may be better off buying this "new one". In many cases, lower quality materials or construction will also have a "benefit" story or endorsement attached to it, along with a higher price.
A prime example of this which had a major effect on the quality of mattresses in general was the introduction of one sided mattresses which were sold as being "beneficial" and "convenient" when in reality they were a way to increase profits and decrease quality at the same time. The "convenience" story that came with it and perhaps most sadly, the consumer acceptance of this heavily promoted story, caused most of the money machines in the industry to quickly follow suit by either lowering the quality of materials in 2 sided mattresses or making one sided versions themselves. These mattresses, with their dramatically reduced manufacturing costs and longevity, were sold at slightly lower prices but nowhere near the level that accurately reflected their quality or manufacturing costs. Pillowtops and eurotops using lower quality materials, usually low grade polyfoam, and many other "features" of the most common mattresses sold today have all been "bought" by consumers for their short term benefits and feel in the store. When they wear out or lose their qualities long before their time, there is always "this years" model which is "better than ever" and designed to "fix the problem" that was created by the same manufacturers in the first place. You will now even see "non pillowtop" mattresses using what is called "higher quality materials" being sold when it is often just less of the same lower quality polyfoam with something else added to justify a "new story". It is an endless cycle of yearly changes and "amazing sales" that continues the trend towards lower quality and increased prices as consumers become more willing to spend even more to make up for the deficiencies of lower quality "name brand" mattresses as the "relatively" better quality mattresses they do produce is being targeted at higher and higher price points and profit levels.
There are a few national brands however that are still run by "mattress people" more than money machines and while their culture is more corporate than privately driven, compared to other national brands they tend to have better value and offer better pricing than the largest brands that co-incidentally often start with "S". Some of these better value national brands however have wide differences in how they are manufactured in different regions as they are often owned and operated by a series of "licensees" with differing values and priorities. It is amazing to see that in certain regions, mattresses that carry these brand names are very different than they are in other regions that are made by different licensees. This variability in quality and the durability of the materials used has made these "mid size", some of them top 10 in terms of sales, a risky proposition if you are not knowledgeable about the differences or are buying them in an area that the manufacturing quality is not as good. They can represent anything from good value to poor value and everything in between. These manufacturers, and the hit and miss nature of the mattresses they sold, was a factor in the "off brands are worse" stories made up by their larger competitors to keep them from gaining ground and market share. The off brand story, while it did have some truth to it when used to describe certain companies, was accepted as "the truth" for all alternate brands by many consumers who didn't know any different and didn't have the knowledge or even know where to find the knowledge to make legitimate comparisons. These consumers more and more began to "play it safe" at the expense of the true higher quality regional and local manufacturers that made high quality mattresses in every area of the country.
While many of the larger national brands can not compete in quality or value with their smaller competitors, there are a few smaller national brands that make more specialized mattresses that do. They are sometimes a little more difficult to find as their distribution network is not as large however with a little research these smaller national brands may well be worth consideration. Some of these are even sold in some of the large chain stores although not with as much floor space and they may try to "steer" you in other directions towards higher profit or more heavily promoted mattresses. These brands can also make good testing grounds for field testing the type of mattress that works best for you.
The "better" national brands can represent good ... but usually not great ... value for those who have little selection in their area (very rare), are in more of a hurry with their mattress purchase, or are more inclined to do "brand shopping" than researching materials and the differences between mattresses and their construction.