Because they assume you've set [email protected] to be filtered directly to spam, and they can easily evade those filters by removing the ±spam part.
Big companies do this. I have signed up for things using a +filter email address, only to receive the emails from that company that is signed up to get at my plane address, without the +filter part.
Big companies do this. I have signed up for things using a +filter email address, only to receive the emails from that company that is signed up to get at my plane address, without the +filter part.