I have no idea why this functionality was never documented, but one thing sys-tweak can do, is bypass games' requirements for a linked Nintendo account, without having to link a real or fake Nintendo account.
This is useful because 1: why link an account if you don't need one? and 2: Nintendo...
btw i feel this a good time to remind you guys that sea of thieves was made by rare, who also made DKC1-3 and DK64, alongside banjo kazooie and conker's bad fur day