Imagine if there was no img tag. If you want images, you have to use a 3rd party plugin, that is really slow and has no standard way to embed it in a page. You can’t easily copy images in this way, and search engines basically have no clue what if it’s an image or a game or anything.
Without this, no images were available.
Then imagine that a browser was released that just let you use this fancy new img tag.
The video (and audio) tag are a logical sensible way for things to work. We shouldn’t need a third party plugin to use a completely standard media format.