Two reasons: 1. people and spammers have no reservations about taking random email address they find and sending stuff to it/selling it to another spammer for them to send stuff to it. 2. E-mail is the second most likely place for a hacker to get a virus into your computer, second only to viruses in the wild (viruses floating around on the internet) and direct vulnerability attacks. Virus writers are very crafty, and getting better and better at fooling the user into believing something is legit when its not and getting the user to give the virus permission to run, which can be as little as clicking an ad in an email. Then there are attachment viruses which load complex viruses into your system to take it over simply by opening the email. Then you have the hoax people that beg for money to help them or enter a business venture with them in exchange for rich rewards. Also, you have your social engineer hackers that can take your e-mail address, go online, find some more info about you and start hacking your online accounts like your bank or social media. There are so many ways a hacker or spammer can reach you with the simple knowledge of your e-mail address, and if you are not educated on how to protect yourself and recognize it, you can very easily be taken down.