Why does double clicking a video make it fullscreen?

I found the flag to disable it, but I’m really curious why the decision was made in the first place. On Chrome and Firefox, l If you double click this example HTML5 : https://www.w3schools.com/html/html5_video.asp, it will go full screen. I’ve always wondered why sometimes click on a video would make it go fullscreen, it’s laggy and annoying for me, even on high-end laptops. On My Mac, as well as in Windows and Fedora VMs.