You're either "aspirational", meaning that you shoot for the expensive Apple products rather than a simple run of the mill PC for status reasons, or you're "thrifty", meaning that since you've blown most of your cash on a few aspirational products, you can only afford Walmart for anything else you want to buy.
Yes, I'm being a bit glib, but there's some truth in that analysis. People in the middle do try to buy some higher end goods in areas they want to signal status on... they do so selectively, but if they can afford it and its a product that makes a desired statement, they go for it. An Apple product that a billionaire would typically buy is often the same model that a middle income earner can buy, yet everyone knows they aren't the cheapest things around. On the other hand, if you're buying expensive in one area, you're also probably buying cheap in other areas, so Walmart, Ross, etc. are on the table for the middle earner as well.
For middle of the road price/products there's less prestige so you don't get that and there's can be debatable quality difference... so... the appeal can be less for something middling.