From their LTT video, it looked like they chose to do Desktop because of the AMD platform (and not the either way around, where they planned a desktop product and then chose AMD strix halo). Apparently setting up the manufacturing pipeline for laptops built on strix halo is expensive as of now and there are only two laptops in the whole market using it. So Frame.work choose to go the desktop route to save on cost while still making the platform available for everyone.