A few... lack of standard transaction identifiers, fixed hours of business with bespoke holiday schedules, use of humans, use of telephones, physical travel to trade shows, printed literature, cold calling/emailing, manual price checks, incapacity to provide actual volume or delivery dates prior to purchase, manual pricing, non-transparent pricing, manual provisioning and re-entry of client and supplier information such as corporate identity, tax, banking and addresses; bait and switch, tedious inefficient reputation systems, lack of machine-readable digital specifications, lack of 3D models, lack of (translated) documentation, material/regulatory/supplier certificates and associated documentation that is impossible or tedious to verify... one could go on.
Supply chain is a black box with people who are aggressively not interested in transparency. So the approach is to model the black box as good as we can, and start cutting away the pieces with automation.