It was clear, but also wrong.
We're looking at 10 vs 12 lanes. Still plenty for 2 M.2 slots, on top of the CPU driven one.
Well... no, because those 10 lanes are shared resources. Saying "10 Lanes is plenty for multiple M.2 slots" completely neglects the fact that you also need to provision the on-board PCIe slots, as well as any on-board devices that utilises those resources such as high-speed networking or WiFi cards. In reality, having a fully-featured board with high speed LAN (2.5GBE, 5GBE or even 10GBE on some boards) as well as onboard Wifi 6 cards will quickly gobble up your available flexible lanes allocation.
Let's say you have 2x4 M.2 slots available, that's 8 lanes, and your extra 2 lanes being used for on-board LAN and on-board Wifi, respectively, now you're out. What happens when your customer want to plug in a PCIe device (say, a capture card, sound card or something similar?). They don't work, and now you have an irate customer wondering why their PCIe card doesn't work, blaming the daft board OEM for making a garbage motherboard.
I suppose board manufacturers could technically implement 3/4/5/6 M.2 slots onboard, and cut out whichever shared PCIe resources with each slots, but as I pointed out earlier, this will lead to customer confusion and ultimately increase rate of returns/RMAs. Nobody likes having their Wifi and/or network ports disabled, SATA ports suddenly cut off, Thunderbolt ports stops working etc... because they plugged in an extra M.2 device or two.