I have been recieving Fons and Porter's magazine for more than a year and I did not subscribe. Somewhere I read that magazines have to prove that they have a certain amount of subscribers to get advertizing. Even if they have to give the magazine away through a mailing list they can claim that it reaches so many people. The advertizing pays for the magazine, subscriptions don't begin to cover the cost.
I remember when I thought that paying for cable TV meant that there would be no commercials. My son-in-law writes for and edits a "trade" magazine. Subscriptions to it are more than $800 a year. I don't think it has any ads.