I've never understood M.2's adoption outside of mobile devices. It's terrible for cooling and even high end devices can suffer performance degradation due to throttling.
For workstation usage the thermals can be an issue but for typical consumer workloads rarely so.
My board only supports one M.2 stick as I figured that would be fine.
I ended up buying an Asus adapter for under £10 as occasionally I want to access two at a time.
But for the vast majority of users a single M.2 slot for storage is fine I suggest and those that want more NVMe can buy adapters.
Why add cost for the majority by standardising on NVMe cards rather than sticks when it only serves a small minority?
There is also definitely a need for at least one or two motherboards to have more SATA ports or 10 GbE. People just can't see outside of their own use case sometimes. 10 GbE cards are much cheaper now but still £100ish. Paying an extra £50-100 for a higher end motherboard that includes this is cost effective for those that want it.
Maybe you can't see beyond your own use case and recognise that is a niche?
It's a competitive field with plenty of high end boards costing big bucks so when there is a strong enough demand they will build them and at a price that fits your use case.