They still have a print magazine, and it's only $19.99 a year AND comes with a "free digital subscription". So I'm not sure why their charging over 2x for a digital-only subscription. Reminds me of something a newly-minted marketing major would attempt..."psychological marketing of only $1 / week!"
There are ads in the print magazine, a lot of them. It's essentially subsidized.
As for specific digital pricing, from what's been written it sounds like a lot of that comes from the need to have monthly pricing, as not everyone wants to buy a year at a time.