I'm pretty sure the publishing rights to much of the Beatles catalog are still a mess, as they have been for years.
That's a good part of the reason their albums took such a long time to appear on CD, such a long time to get digitally remastered, and such a long time to appear on any digital distribution channel -- and when that finally happened, it was still locked exclusively to iTunes through much of 2011.
I'm not sure where the exclusivity deal currently stands but the parties involved in releasing the catalog weren't terribly keen on digital distribution to begin with, so I wouldn't expect any kind of rapid movement to other digital channels. In this case, unfortunately, the fault lies very much with the artist... or those responsible for handling their music, anyway.
