What is going on now that so many bands are selling their catalogues? Changes in taxes or royalties or copyright law?
Personally if I was a creditor of the firms buying these rights, I would be concerned. I don't see how they'll recoup. Consider Elvis - his star is fading and in 20 years he'll be forgotten. Will anyone care about Springsteen in 20 years/after he's dead? It's not like he influenced anyone younger than 45.
They are making no money on the songs. People are not buying physical copies of CDs / LPs in large numbers, they are streaming. And the revenue the artists get from streaming is a pittance. Basically for most artists a large up-front lump sum is far favorable to a trickle for the rest of your life if you want to live a decent lifestyle and still leave something to your heirs.