"but why wouldn't you consider that a core part of your business worth investing into"
Yes, that's true, and every organization of any size (one sufficiently large enough to implement SAP) will have experts in those domains. The problem is that implementing them in software is a large task - definitely not impossible, or even extremely difficult (it's just CRUD on a grand scale), but you need software that can change quickly when new legislation is implemented, etc. Painful, and the reason why so many do implement a COTS ERP. Hell, even Google run SAP S/4HANA these days (they migrated off Oracle ERP AFAIK).
Yes, that's true, and every organization of any size (one sufficiently large enough to implement SAP) will have experts in those domains. The problem is that implementing them in software is a large task - definitely not impossible, or even extremely difficult (it's just CRUD on a grand scale), but you need software that can change quickly when new legislation is implemented, etc. Painful, and the reason why so many do implement a COTS ERP. Hell, even Google run SAP S/4HANA these days (they migrated off Oracle ERP AFAIK).