Disney are very clever with their flims on video and DVD.
They release a film on video (as was) or DVD, and then sell it for a year or so, and then STOP making the Videos / DVDs for that film and put it back in the vault.
They then release it 3 or 4 years later again, and so the cycle continues.
So this means it makes their films have a rarity value as if you dont buy it when it is out you either have to pay at lot for it, or wait till it comes out again next time on DVD.
This is why it is a good idea to grab a Disney film when it is out or you may have to wait a while to buy it again.