RAM bandwidth is improving a lot faster than its latency. (The latter is almost as stagnant as max CPU clock frequencies.)
They downclock the CPU on mobile devices as the battery ages, to keep the CPU from browning out so you
My system, made in 2013, won't be supported by the next OS release this coming fall, but they usually continue security updates at least one release behind. That's basically ten years of hardware support.
Keep in mind that Windows 10 came out in 2015. A ton of manufacturers simply did not support windows 10 on hardware sold before it, because win10 coming out helps them move new PCs.
Apple leads the industry in using slave labour to create disposable fashion items.
https://9to5mac.com/2021/05/10/seven-apple-suppliers-alleged...
We've solved the storage latency and throughout bottlenecks, scheduling, and CPU core counts, so we don't really need beaucoups of RAM for a functional laptop.
RAM bandwidth doubles with each generation and throughout and latency improve, so less is needed for the same performance.
Batteries are relatively inexpensive to replace through the vendor are improved in energy density, energy density, and cycles, so there's not a big advantage to buying aftermarket even though you can.
For 2014-2016 Macs with flash storage, they're still pretty great to excellent machines. The greatest detriment to the longevity of 2017-2019 Macs is that they contain Intel components, and that every release of MacOS since High Sierra has been designed adversarial against their security flaws. Costco was practically giving away Intel iMacs recently, offering them almost half off.
Also, I remember benchmarking on apfs post-mitigations and seeing up to a 40% performance loss on some syscalls, which translated to an unusable computer on dual core Intels or anything with mechanical storage. How would upgrading components have helped then?