To add to your rant with my two cents:
I personally bit the bullet and went full workstation with WRX90. Absolutely no constraints there when it comes to bandwidth and physical slot count (except my RTX 4090 which takes up 3 slots only to use 16 lanes @ PCIe 4.0). To be fair, TRX50 would have sufficed for me if I was being practical, but I cave to my wants when it comes to PCs.
I think what AMD had before was fine, which is evident since they went from having a unified Threadripper lineup to having a PRO lineup for Zen 2 (with the 3000 series), thinking they could do a PRO-only lineup (which people got really mad about), and then came back with the current gen of a dual lineup again. Except, the problem is that the HEDT/non-PRO CPUs are still stupid expensive. This wouldn’t be an issue at all if they had just made the non-PRO CPUs half as expensive and maybe just only had a 32-core CPU as the top-end if they wanted to protect their PRO sales from cannibalization (if you’re looking at a 64-core CPU anyway, you’re probably going to go full PRO is what I would think but maybe there is someone out there who just wants many cores on a cheaper platform).
Seeing as you’re on X99, the top-end mainstream motherboards were never meant for the prosumer userbase that you or I am a part of. AMD already has a platform that suits our needs (TRX50), it’s just that the CPUs are priced so badly they’re out of most people’s reach. I remember when I got my 2950X for a mere $750 back in the day; I’m pretty sure the MSRP of the 7960X is twice that.
On the topic of “just create another motherboard” there was just this thread (ha) last week that discusses your issue. Assuming this reply is true, it comes down to cost of manufacturing to one spec of 24 PCIe lanes (and then ASUS, et al. decide what to do with them). And so then it really still is AMD’s fault: there’s no point in having more physical slots when you have to support, for example, USB4, PCIe 5.0 for the top PCIe slot (even though GPUs don’t saturate even PCIe 4.0 x16), a couple of PCIe 5.0 M.2 slots, etc, etc.
TL;DR: This entire conversation wouldn’t exist if the HEDT CPUs were cheaper. Motherboards that cost $800 is not the problem; CPUs that start at the cost of the RTX 4090 MSRP are.