Not necessarily true. The place I work at does the payroll with some cheaper payroll ERP. Most other things...well let's just say a programmer to make the entire thing was cheaper and more effective. The ERP has to interface with various NFC and barcode scanners, ticket printers, etc other companies appliance interfaces, the consultancy costs to adapt and existing erp and make it keep track of the entire production process and it's unique quirks would be trough the roof and make any subsequent version upgrade unmanageable cost and time wise.