They’re still cheaper for the most part – but, like electronic music, more expensive than I think they should be.
It’s because of the rights concern and paying up-front for free-loaders. Much of the cost is built in as payment for the artistic investment of the artist and producers and the copyrights and licenses for that – you’re essentially buying a license to “perform” or “exhibit” the art, although limited to private non-commercial manners of it.
But also, releasing things electronically ensures that there will be copying of it and distribution of it in a manner that means loss to the company releasing it. Many people will pirate/share in a manner unintended and not allowed by their “license.” So, you tack on some of that to the price to cover for that.