I once considered buying a product. Got as far as putting my contact and address in (no account).
I've changed my mind last minute, and they've been badgering me every since, clearly having recorded my details for marketing purposes before I ever pressed a single button.
They just blatantly ignore your preferences because they know there will be no consequences.
The one thing that generally works well in Canada at least is that they must provide a way to unsubscribe at the bottom of the email. The complaint process is relatively simple and the fines for violations are steep.