Why mbp keyboard light stays on while playing video in fullscreen? I noticed macbook pro keyboard light stays on while playing video in fullscreen, on youtube and vlc. Wouldn't be better if apple auto turn it off (since I'm not using keyboard while watching movies)?

I'm using latest macOS on mbp 15 retina.

Keyboard light works normally in other situations, if I stop typing for a while it goes off.
YouTube is a web-based video platform and VLC is a 3rd party program. These are not Apple-made applications and so may not be built specifically for the hardware you are using.

You can control the MacBook Pro keyboard lighting on your F5 and F6 keys for these 3rd party applications.