I was struck by your comment about the short life-cycles of Chinese IEMs. I wonder if this is driven, in part, by manufacturing and supply chain problems. If a brand orders n thousand IEMs from a manufacturer and sales are below expectations, perhaps it's cheaper to abandon that particular model rather than order another n thousand just to keep it in the brand catalogue.
I suspect that Chinese OEMs will gladly run off as many items as required, in whatever configuration, but re-tooling or re-configuring the assembly line must incur a significant cost.
The profit margin on budget IEMs must be slim. Perhaps there comes a point when a brand decides that the publicity value of a best-selling item no longer outweighs the hit in income.
It's a tad more complicated than that and I do know people that make IEMs.
The quality control is all over the map for Chinese IEMs. So you quasi roll the dice no matter what price point you're buying at. Then there is the "waifu issue". To be blunt, Moondrop can sell four versions or more of what is pretty much the same product by slightly changing the pain job and giving you a different anime girl with an up skirt shot on the box. They are cheap enough you can collect them, just for incels who want a waifu. The companies know this and push it.
It boils down to that American/European/Japanse brands are trying to make something that lasts and they expect you to buy one or two. Chinese makers throw quasi child porn on the brands and trust you will want to pokemon catch them all then and give two shits beyond that. But they are cheap.
Giant headphones has it´s market share i guess.
For at home usage, with a proper dac, amp, and all that jazz they are better than IEMs. Especially when it comes to sound stage. They compete with bookshelf or even tower speakers that can cost 5-10k per speaker. Then there is the amp issue. DAC gonna DAC, and source gonna source, but the cost of an amp will skyrocket for a good set of speakers. 5k is sort of mid range, you can clear 10k easy. Headphone amps come in at half that.
There's also the noise issue. I've got a technics turntable (SL1200 series these retail from 1000-2500 depending on the model) with an Ortofon B Black stylus (this is 1k alone) with Focal Tower speakers (kiss another 5k gone) and a several thousand dollar amp pushing. As amazing as it sounds everyone in my condo building is going to hear it. So I can't use it all the time. By contrast I can plug my headphones into the same thing and not cause the dogs to start barking all over the building and sounding like I started WW3.
For work and the train or plane, I have IEMs. But even my souped up Empire Ears (1350 for the IEMs, 250 for the cable, 100 for the dac/amp combo) do not compete with over ears, and those over ears do not compete with speakers.