Rhubarb the fraudstars dont know you use Paypal or anything else for that matter. They just mass email people. If one in 10000 has an account and then out of every 100 that has an account and goes on to put in their details then they can make a lot of money for very little bar a small bit of time on making up the emails.
I constantly get phishing and other spam to my secondary address. Checked about once a month but only used to sign up to sites such as dabs to avoid getting all the trash.
My main one gets quite a bit too.