I always felt like those click to unsubscribe links were nothing more than a "please prove to us with certainty that this is an actively used account so we can set a sticky bit on it and sell that info for $$$"
That’s a commonly held idea for spam emails. This is about services you’ve signed up and pay for on a recurring basis, and was targeted at companies who make it very easy to open an account, but then require byzantine methods to cancel.