Nothing wrong with thinness when it is in service of a quantifiable improvement in product performance, user experience, etc. Not only did no one ask for an ultra-thin desktop computer, but it is counter-productive to the usability of the device. A thin laptop? great. A thin mobile phone? cool. A desktop computer doesn't move around or have a need to be 11.5mm thin. Especially when it comes at the cost of features.
I don't dismiss wireless at all. Wireless enables many great things. It's not as robust, fast, or error-free as wired, but the benefits usually outweigh those drawbacks. I would never blindly embrace all things wireless as being "better" - they just enable certain flexibility that makes the tradeoffs often worth it. To claim that the tradeoffs are ALWAYS worth it, and wireless is always better, would be to ignore reality.
The last gen iMacs were pretty thin...getting thinner with the new 24" didn't achieve any particular functional goal other than to show that Apple can do it. What was lost were significant features. The whole point of an all-in-one was to simplify and integrate all the features users need into an elegant package. With the new iMac, Apple literally took the internal power supply out and put it on the user's desk or floor, just to achieve thinness of the display. That's the difference. Pushing the bounds of tech is great, but it has to be in pursuit of a useful goal.
The iMac is and has been for about a decade, a laptop with a huge monitor attached. It's not a real desktop and hasn't been for a while. Therefore all the parts and design ethos are pretty much shared between whatever Apple is doing with laptop technology with the added benefit of better heat handling and fixed power.
Obviously when they moved the laptops to m1 and basically turned their laptops into mobile phones / iPads, they weren't going to start making them thicker. Where would be the benefits in that for them? You make your margins by reusing design across different product lines. I kind of think you hear the word "desktop" and think that iMac is a real desktop. It isn't.
Also, looking at the emphasis on colours, its not as if this is designed for pro's is it? 95% of iMac buyers will want a general purpose computer than looks nice in their home or office and that's about it. And so how it looks is paramount, hence its thin and nice looking, because that's what the public who buy these products value.
Having an external power supply is not the worst thing in the world, it sits on the floor away from view. It also allows for ethernet connection without the dodgy cable looping over the desk, so its really not bad.
Anyway, your missing my original point. Spending energy pushing boundaries may not have the desired effect for some pro's. But its not wasted energy. A lot of what they found will be used in other products.
Finally, having good looking products that are not slaves to functionality is exactly why Apple is successful. That's literally Steve Jobs' mantra. Let everyone else do the bulky, million ports, replaceable everything designs like they used to do, and let apple design for people who compromise for the aesthetic. Design in general, whether its clothes, houses, whatever is full of non practical choices because they look good. Because that's how a lot of humans are. Apple just reflects that part of humanity.