A multisig wallet requires several keys to agree before funds move: two of three, three of five, any threshold the holders set. It converts key loss and key theft from catastrophes into quorum problems, one compromised key is an incident report, not a heist.
The cost is coordination: every movement needs signatures from keys that should live in different places, with different people or devices holding them. That is exactly the property a treasury wants and a coffee wallet does not.
Merchants can point checkouts at multisig destinations, the non-custodial architecture accepts any valid address, so the quorum policy travels with the funds rather than with the platform.
Every term behind the rails, the assets, and the settlement.