Soif all this is true and custom elements are completely valid in all modern browsers without any Javascript requiredthen why on earth are we stuck writing 90s-era DIVs everywhere?! It’s semantically meaningless and only serves as a raw vessel for styling purposes!

The answer isinertia and ignorance.

Source: Custom Elements Everywhere for Page Layout, Parts I and II - DEV Community

So simple. I wonder if this will be more common in the future.