Who is squatting IPv4 addresses?

You would very likely find that there is very little actual squatting of IPV4 addresses. The big problem with IPV4 addresses is that there were so few of them to start with.

Though back then, in the early 1990s, when I first got my 256-host block we were still being amazed that there were A WHOLE MILLION hosts on the Internet, and surely 4 billion or so addresses could never run out. (That's what Arthur C. Clarke called 'A Failure of Imagination' in his book "Profiles of the Future".)

In my own case, I have been asked many times by the regional IP-address allocator (APNIC) whether I would be willing to allow my block of hosts to be given back for re-allocation.