Why? Because your standard video player (VLC, Windows Media Player, or QuickTime) does not understand how to "link" the digital signal to your polarized hardware.
Tell the player how the video is stored (usually Side-by-Side). 3d video player for polarized glasses link
(like a 3D TV or monitor) that has a physical polarizing layer. Most standard computer monitors cannot use polarized glasses via software alone; they instead require anaglyph (red/cyan) glasses Windows Media Player
Bino is a great open-source option for those on Windows, macOS, or Linux. It is lightweight and focuses strictly on high-quality 3D video playback. 3d video player for polarized glasses link