Ask HN: Why is spacebar still Page Down in browsers

Pardon my ignorance, but spacebar was next page on msdos systems while enter was next line, that still hasn't made much sense to me since we had PgDown key on keyboard. I always use PgDown and PgUp keys in browsers. When i want to pause videos (they have to be in focus in order to pause) i get the same result as if i pressed PgDown. I've got used to using spacebar as "space" in text editors and pause in video players. The question is what made developers do this? Kiosks? EDIT: Shouldn't there be a standard that defines keybinds in apps? End users do get confused-