You can look at this as a money-grabbing enterprise, but I have a different take: Ringo and Paul have an emotional connection with John and George that none of us have, and I sincerely believe that they wanted to share a "lost" song with the world, now that the technology exists to make it sound presentable.
I saw Paul in concert last year, and there was the bit where he was able to sing harmony "with" John on "I've Got a Feeling" because the tools now exist to isolate John's voice in the rooftop concert footage. It sure seemed that Paul got a real thrill from "reconnecting" with John that way.
My guess is that Paul and Ringo, now in their '80s, don't want to let opportunities like this slip by. Not opportunities to rake in more cash, but opportunities to honor their mates.