> It’s almost universally true.

It’s not. I give a unique email address to every service I register with, which means I can see who is leaking my email address. Very few of them leak my email address at all, and those that do tend to do so involuntarily through data breaches.

The other main factors in spam are the sleazeballs at Apollo, ZoomInfo, et al., services that use my email address internally for more than I consented (if I use my email address to register for a service, this does not permit that service to add me to their product mailing list), and the spammers who guess email addresses based on LinkedIn info (e.g. name + company domain).

The number of services who appear to take an email address I have given them and sell it appear to be extremely rare.