Because the size of the market was/is so small that you're actually able to corner it. Oil or Treasury futures are far too big that no single person could ever corner it.
> Treasury futures are far too big that no single person could ever corner it.
Well, you'd think, but squeezing the CTD bond was completely accepted practice well into the noughties until PIMCO flew too close to the sun and faced regulatory wrath.
There are many other small markets as well, and yet, this law is not called the "Don't Corner Small Markets Act".
Though the Hunt brothers made a pretty good run at the Silver market in 1980.