Its quite a mix, we have become a nation of disposables. We treat products much differently than previous generations (I'm not talking 30 year olds) because ever since the baby boomers, things are just more likely to be replaced, thrown away working, or forgotten. We can buy a $20 blender for a party and throw it away after and not feel bad about it, because it was only $20, and it looks cheap but we only needed it for the day, and where would we store it, and how often will we use it when we have a ninja mini blender.
This almost applies to everything, personally I don't care about lifetime warranties on tools. Partially because who knows if the company will actually honor it, and honestly, I'd probably lose it before I ever broke it.
Clothes, they are typically out of fashion before they are worn out, I still have tshirts in good condition from 20 years ago.
Even electronics, are disposable where you can actually identify the lifespan of specific products, most people won't have a cell phone older than 3 years, and most people won't use a computer over 5 years old, and these were hundreds if not thousand dollar investments for most of us.
How does this affect Sears? Sears was a company that stood by their products, and had quality (even if you had to pay more) and it was a company that was going to be around "forever" so the lifetime warranty was worth it. That customer base hardly exists anymore, and we all know that they no longer have quality or customer service, so we are left with paying a premium for "less"
Other retailers have been more specialized in product (best buy, Kohls) or price (dollar general) or have a broader selection (Amazon)
This allows people more choice in what they can afford for the time they need to use a product.
As the other comment reflected there is also perception Kmart is cheap (quality wise), and I feel I would get the same products as a dollar general, but I would assume dollar general would be cheaper (cost wise)
Long gone are the days where the quote "If Sears doesn't have it, you don't want it" can work. Because it did work for years. Companies would kill to get their products in Sears because it reflected well on them, it was better than flying an american flag in your commercials!