Why does the service use many of its tags?

Question

Frontend

Good afternoon. It has been interesting for a long time, but not so much to find the answer: why does YouTube's versioning consist of a bunch of their personal tags? For example, instead of div/span they can use yt-formatted-string
What is the reason? This has been a phenomenon for quite some time now.
Did they deviate from partial support for browser tags and create their own with their own settings? But why?

Answer 1

https://code.tutsplus.com/ru/tutorials/extending-t...
https://learn.javascript.ru/custom-elements

https://developers.google.com/web/fundamentals/web.. https :
//developer.mozilla.org/en-US/docs/Web/Web_C...