People are using your email address as a burner. The dots in gmail are ignored. Another really fun one: dicksmallz+IsADoucher@gmail.com will ALSO deliver to you. Anything after the + is ignored. So you can use your email and add a tag, e.g. DickSmallz+surly@gmail.com to register for sites and filter accordingly.
I've got the same problem with some asshat in Wisconsin that has been using my email address to register for everything. Dumb ass even registered for Tax Slayer using my email address. I went and reset his password, changed the 2FA phone device, and locked him out. I've now got his address and SSN, among other things, after he's been doing this crap for 5 years now. He's adopted a dog under my email, sent his kid to school and registered him under my email (took everything I had not to reply back to them and tell the school to unenroll him). And somehow, his phone number is always delisted when I try to call him to tell him to stop.