> Intel's consumer processors (and therefore the mainboards/chipsets) used to have four memory channels, but around the year 2020 this was suddenly limited to two channels since the 12th generation (AMD's consumer processors had always two channels, with exception of Threadriper?).
You need to re-check your sources. When AMD started doing integrated memory controllers in 2003, they had Socket 754 (single channel / 64-bit wide) for low-end consumer CPUs and Socket 940 (dual channel / 128-bit wide) for server and enthusiast destkop CPUs, but less than a year later they introduced Socket 939 (128-bit) and since then their mainstream desktop CPU sockets have all had a 128-bit wide memory interface. When Intel later also moved their memory controller from the motherboard to the CPU, they also used a 128-bit wide memory bus (starting with LGA 1156 in 2008).
There's never been a desktop CPU socket with a memory bus wider than 128 bits that wasn't a high-end/workstation/server counterpart to a mainstream consumer platform that used only a 128-bit wide memory bus. As far as I can tell, the CPU sockets supporting integrated graphics have all used a 128-bit wide memory bus. Pretty much all of the growth of desktop CPU core counts from dual core up to today's 16+ core parts has been working with the same bus width, and increased DRAM bandwidth to feed those extra cores has been entirely from running at higher speeds over the same number of wires.
What has regressed is that the enthusiast-oriented high-end desktop CPUs derived from server/workstation parts are much more expensive and less frequently updated than they used to be. Intel hasn't done a consumer-branded variant of their workstation CPUs in several generations; they've only been selling those parts under the Xeon branding. AMD's Threadripper line got split into Threadripper and Threadripper PRO, but the non-PRO parts have a higher starting price than early Threadripper generations, and the Zen 3 generation didn't get non-PRO Threadrippers.