Your description of a drink that takes the world by storm, increasing in market share but dropping in quality may be roughly accurate analogy for a lot of consumer goods, but even in this telling the market is improving if that drink is displacing even lower-quality competition.
In terms of non-alcoholic drinks sold in coolers in convenience stores and grocery stores, we've seen the steady march of improving products as an average across the shelves, even if the same product name might be getting worse. In the 80's, the dominant market share for orange juice in grocery stores was frozen cans to be mixed with water at home. But Tropicana and Florida Natural and a few other brands made a splash with not-from-concentrate orange juice. Old brands like Minute Maid got in on the action, and new brands like Simply rose up, too.
Now, it might be that these brands have gotten cheap with stuff since dominating market share. But if you look at who they took that market share from, it's unquestionably a lower quality product they've displaced.
Across the beverage industry as a whole, you've got a whole bunch of newer higher priced drinks, where the unfathomably expensive for 2000 Red Bull is basically the middle of the pack for energy drinks, and where there are so many beverages that cost several times as much as Coca Cola.
So that's a story of a forward march in higher prices for qualitatively preferred items, over that amount of time. This story I do think applies to processed food and drink, as well as electronics, prepared food, home furnishings, and cars. We expect a lot higher quality every year, as the things get more expensive, and we feel annoyed that any particular brand or model seems to be slipping in quality while we as a consumer market tend to move up the chain.
We're angry that streaming seems to be slipping back to cable-like quality, when streaming as of 2024 is still a much better value proposition than cable in 2014. The displacement is happening in two directions, for a net benefit to the consumer in a way that doesn't feel like a benefit. Same with music, video games, etc.
The real story is that housing, education, healthcare, and dependent care (both childcare and elder care) have gone up so much faster than inflation that these things are finally squeezing normal people out of their comfort zones right when the other stuff stopped dropping in price as much as before.