@Evv1L @frameworkcomputer Memory and storage are optional parts that you can add yourself. If you price out DIY with similar parts to pre-built, including the Windows 11 Pro license which is mandatory on the pre-built, you'll find they are fairly close.
I imagine they disassemble since they need the parts for QC, even if that DIY order doesn't actually come with them. Otherwise they end up with too many SKUs.