Because it doesn't meet the requirements for L2. I think L2 implementations are required to block software screen recording, for example, and there isn't really

Because it doesn't meet the requirements for L2. I think L2 implementations are required to block software screen recording, for example, and there isn't really any practical way to enforce that on an open platform. Windows/Android/iOS have special support for compositing protected content so if you try to read the framebuffer back the content just shows up as a black rectangle.