If you have a sign up form it doesn't matter if they list the husband's name or the wife's name because either one is valid to sign up.
If you have a cancel form it does matter, because it has to match the one used to sign up or they don't know who you are, even if the customer doesn't remember which one they used. Or any number of other issues with matching the request to a subscription.
Humans can sort this out, but then you can't cancel on the website. Computers can also sort this out, but then you need sophisticated programming instead of a basic form. It's not symmetrical.
Ah yes, let's allow businesses to employ dark patterns to profit at the expens of unwilling customers because otherwise they might need to put in a little effort to deal with hypothetical edge cases.
The businesses using dark patterns are disproportionately large corporations. The ones that have trouble implementing a regulation which is airtight against corporate lawyer tricks are the small ones. That implies the obvious solution that you make the rules specific to the large corporations, e.g. ones with more than 1000 employees. But the rules typically aren't written to do that, and as long as that continues you're going to get resistance from the very large number of small businesses you're screwing.
If you have a cancel form it does matter, because it has to match the one used to sign up or they don't know who you are, even if the customer doesn't remember which one they used. Or any number of other issues with matching the request to a subscription.
Humans can sort this out, but then you can't cancel on the website. Computers can also sort this out, but then you need sophisticated programming instead of a basic form. It's not symmetrical.