The answer is: to solve several problems:
1, Money. To buy and make magazine(s), to know and host the newest works in literature & arts, is something that implies “to have lot of money”. Web is quite free.
2, Distribution + links between authors. Too many authors and texts do not reach lots of authors and texts. Web does, web works.
3. Amount of materials. To store files is easier than to store paper reviews and books. The space in the real world is ‘more real’ than in the net.
Maybe the wider net community and ring of magazines online is, by birth, English speaking. Due to the need of a whole world extension, people talking in English meet on the net and make magazines using the net.
The opportunity of uploads is another important element and a powerful enrichment. You can post a pdf document, a Word one, a gif, or a jpg image or a jpg text or some mixed works also.
Paper gives you more limitations, a sheet has borders. A Word document is a virtually unending page.
On the other hand, a good thing in a Gutenberg state of mind consists in having a deep and enigmatic sense of limit, and a consequent trait or faculty in generating abstract/quite-dreamed (ir)rational materials. When something gives you limits and edges, you let your voice and glance go further anyhow; and you may really get to a REM mood which drives you to dreamed-but-rational thoughts.
In a limitless universe, where materials grow indefinitely being all linked to an infinity of things, this does not happen. The sense and scene of an unlimited stack of items abolishes the margin of REM waves production. To provide strong echoes’ sounds you must have empty spaces.
Plenty = opportunities. But it’s a new problem too.
It’s not accident that magazines online are often six-month ones, o four-month.
You need space to let texts produce echoes in reader’s imagination. This is a kind of heritage or influence of what I called a Gutenberg state of mind.