I am going to mirror what someone else said.
#1) They need it in print. Webzines are a dime a dozen, and 95%-99% of gamers do not even KNOW that a Dragon Magazine or any thing similar to it even exists. The advertising for it is poor, the usage of it is poor, and thus it's influence is limited.
Part of this is advertising, but part of this is simply visibility. Put it in a subscription service (for example, magazine subscriptions are advertised via Amazon) that spreads it's availability around and puts it in waiting rooms and offices. There are a TON of businessmen, dentists, lawyers, and others these days that have been or are gamers. Catering to them with a magazine for D&D is easier than it has ever been. This not only appeals to their hobbies of the past or today, but is basically free advertising for WotC.
In addition, there are a ton of people that prefer to get in print magazines (for example, I still get National Geographic, even if I don't read it much myself anymore. I do have others who read it while sitting around in my living room or elsewhere, and it's nice to actually browse through it in print).
This doesn't negate an online presence for a magazine, but having it in print can spread awareness and is useful.
Printing on demand for a subscription actually is a calculated cost that done correctly will NOT lose money, but actually make more than normal. If utilized as an advertising recourse, it can actually increase the rest of sales as well.