That’s because those “people” are either larping students or kids that want to become programmers. I have never in my 10 year career met a person who said “yeah, I learn my craft from Fireship videos”.
Videos are sort of easier to produce (via screen capture), and are much easier to show the effect of FE things: look, we write code like this, now we can click here, and the page reacts that way. No need to muck with JSFiddle or something.
I'm not a fan of videos as a reference medium, but they can be elucidating to those who needs more hand-holding, literally "click here, see the result". Back in the day, a few short videos about Blender helped me quite bit to grasp certain things that were not obvious from descriptions.