I get spam from legitimate companies, probably because they don't validate the email addresses their customers give them, and thus incorrectly assume that I have a business relationship with them. I do not, thus it's spam.

Companies need to validate email addresses.

I get AT&T bills, OnStar notifications, etc. I have never used any of their services. Someone else probably signed up with my email address.

Additionally, other companies are violating the CAN SPAM Act by hiding the unsubscribe ability behind a log in. Nextdoor does this.