There's three Winevine tiers, L1, L2 and L3, which generally correspond to 4K, 1080p and 720p respectively though it depends on the service. L3 is what you get on Linux. L2 is supposed to be more secure than L3 but AFAICT it makes little difference to piracy groups, L1 is the only actual roadblock for them.
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.
DRM only really works if you're not root on your own machine, and with Linux you're always root on your own machine. Quite frankly I think DRM (the normalization of rootkits) is dangerous.
