Mail delivery is heavily subsidised, so it makes sense to send out free mags.

The publisher is paid by advertisers to get the mag into a certain number of peoples hands, even if that means giving it away. If they are ethical they will not report your subscription as not being a paid subscription.

The cost of send out a mag is much less than the profit from a possible future subscription. The free mag is a kind of advertising or pruduct sample.

You are considered an opinion leader. Your lemming friends will subscribe so they can be cool like you. Just like you buy name brand stuff to be cool like a celebrity.

Their mail list is all screwed up and people are getting the mag who have not paid.