The vast majority of current web development project don't need to go anywhere near the bleeding edge "still in development" browser APIs.
Your argument makes no sense in the year 2018.
Depends, if they are trying to compete with native apps or not.
Of course if they just stick with the ideal model of hypertext documents, with a little bit of JS, it doesn't make sense.
As for web apps, I am ok with them, provided they run on the browser I have already installed, instead of faking native apps.
https://ishoudinireadyyet.com/
https://www.webcomponents.org/
https://hangouts.google.com/
Also, to use those standards, one needs to have access to latest browser versions, which never happens beyond controlled environments.
So typical web development always needs Modernizr, Babel, Polyfills (when possible) around.