One technical reason is that AAA games would require a complete rethinking of their asset loading strategy, since they'd basically have to use the internet as a very slow and very unreliable hard disc to stream their assets from (which basically means you can't stream the kind of high resolution assets expected of AAA games at all, so you'll have to find a simplified graphics style that looks explicitely 'non-AAA').
You don't want to wait minutes or even hours to download all assets before the game can start (and then again next time because the browser can't cache so much data).
TL;DR: the web platform is different enough from native platforms that ports of bleeding edge games (even from 10 years ago) are not feasible. You'd have to design the entire game around the web platform limitations, which are mainly asset streaming limitations.
But that doesn't happen because there's no working monetisation strategy for 'high profile games' on the web platform, the whole business side is just way too risky (outside some niches which mainly focus on casual F2P games).
The 3D API is only a very small part of the entire problem space (and by far not the most important).
In the end it's mostly about the missing 'business opportunity'. If there would be money in (non-trivial) web games, the games would come.
You don't want to wait minutes or even hours to download all assets before the game can start (and then again next time because the browser can't cache so much data).
TL;DR: the web platform is different enough from native platforms that ports of bleeding edge games (even from 10 years ago) are not feasible. You'd have to design the entire game around the web platform limitations, which are mainly asset streaming limitations.
But that doesn't happen because there's no working monetisation strategy for 'high profile games' on the web platform, the whole business side is just way too risky (outside some niches which mainly focus on casual F2P games).
The 3D API is only a very small part of the entire problem space (and by far not the most important).
In the end it's mostly about the missing 'business opportunity'. If there would be money in (non-trivial) web games, the games would come.