Even web devs learned this a long time ago. And no we are not staying in our own bubble. As you probably know web is huge and it's hard to know all best practices. Even in the language you are programming there are probably things you don't know. People learn all the time, people start learning all the time.

It feels like people have superiority complex over front-end devs and lately specifically javascript. It bothers me. What if you tell me your language of choice and every time I see it mentioned somewhere I will post some random "intellectual question" combined with stereotype that will make you feel stupid and just demotivate you a bit. Maybe I am missing something but your comment made me feel that way.

To answer your question fully; In my opinion it's because there is no single entity that owns the web. No one controls which things should be deprecated or continued, that's why it's happening much slower because big guys have to come to an agreement. Apple provides best practices for iOS, Google for Android,... MDN is a good resource but there is no official "BEST WEB PRACTICES" entity.

I feel you took my comment too personal. Is wasn't an insult to anyone.

It was a lot more difficult in the jQuery days. Requiring a script often did non-obvious things (global variables, touching the DOM, registering even listeners, etc).