It's not just a description of the latest set of motherboards having fewer than five PCIe slots. It's a description of the PC expansion market as a whole, including the fact that many things that would've been PCIe expansion cards "back in the day" are now built into motherboards, sold as USB/Thunderbolt devices, and/or available as M.2 cards. The journey of discovery it took for me to realize this was simply kicked off by the dearth of PCIe slots on announced AM5 motherboards.