How do spammers get your email address? They have many sources, but one way is through harvesting email addresses in plain-text from websites. HTML entities are an encoded way to represemt all of the characters in the extended character sets. The average Spam spidering script won't be looking for these characters.
Which lools like an email address?
To a web browser, they're identical. To a harvesting script, they're not. Technically, they could attempt to decode every page they look at, on the off-chance, but they don't because it's too much of a hassle for too little reward.