Why does Do You Need a Blockchain? (Wüst & Gervais, 2017) argue that most Supply Chain Management (SCM) deployments don't actually need a blockchain?

Question

Accepted Answer

Because SCM's real weak point is the physical-to-digital interface: if you can't trust the humans/sensors entering data, the blockchain can't fix it; and if you can trust them, a shared database already suffices.
Run SCM through the methodology: it stores state, has multiple writers (companies owning shares of the product), and writers are generally known. So the pivotal question is can all writers be trusted? SCM has an inherent problem — a person or machine has to register that a good physically arrived, in the right quality. Two outcomes, both undercutting the blockchain:

If those data-entry parties aren't trusted, any of them can feed false data on-chain; the whole chain is compromised regardless of the ledger. The blockchain guarantees the data wasn't altered after entry, not that it was true at entry.
If they are trusted, a plain shared database works fine.

The paper even notes Skuchain (built on Hyperledger Fabric) conceded that a single trusted database would satisfy most SCM needs. This physical/digital gap is the recurring theme — the same problem re-appears in IoT.
Go deeper:

Supply chain (Wikipedia) — the multi-party goods-and-data flow whose physical-to-digital entry step the ledger can't secure.