That’s not true, you must be comparing unlike boards and machines.
a 7640 mainboard is $380 (https://frame.work/products/mainboard-amd-ryzen-7040-series?...) and a 7640 chassis (with no memory, ssd, or expansion bays) is $750 (https://frame.work/products/laptop-diy-13-gen-amd/configurat...)
Another example, the ai 7 350 mainboard is $700, and a bare chassis is $1,230.