[coolandsmartrr]

It's probably posted without permission, but I don't think there's a strong incentive for rights holders to pursue copyright enforcement.

Screenplays are often meant for circulation, albeit in smaller circles within Hollywood and film industry personnel (producer and director mainly). The money is recouped when the finished film screens.

Of course, you can always buy the screenplay for personal reading to support their creators. It's often on Amazon. I used to read some at my library.