The Pirate Bay was caught with that too, though their explanation was that by letting them mine cryptocurrency on your machine, it would eliminate the need for ads.
“Let us know what you think in the comments. Do you want ads or do you want to give away a few of your CPU cycles every time you visit the site? Of course the mining can be blocked by a normal ad-blocker.”
I have discovered that coinhive is finding its way into a wide number of sites. This is probably due to the frustration with ad income.