Short answer ~ money. It is no longer economically viable to produce printed magazines, unless you have a large base of paying subscribers. If you don't have that, a digital magazine is cheaper to produce, but it's still not 'free' and somebody has to pay editorial wages (get advertisers to pay for content inclusion, blabla). In the online world, you can recoup these costs by extracting data from subscribers, and selling same to marketing organizations.
Which magazine btw?
Bookmarks