I'm missing a poll on why people DON'T subscribe.
- Because the pop-up or overlay asking me to is blocking my access to content
- Because I don't know (and reading miles of legalese is not my hobby) if you will sell my address
- Because I am quite capable to visit the site again if I want to know if they have something new
- Because there usually isn't anything interesting in them anyway
- Because it's mostly just an advertisement to come visit a site and watch ads

Edit: This in general, not specifically YOUR newsletter. I don't know yours but others have soured me for yours.