It's a combination of problems but IMHO mostly due to things like: lack of tooling, immaturity of graphics libraries and especially immaturity of WebGL2 in thos

It's a combination of problems but IMHO mostly due to things like: lack of tooling, immaturity of graphics libraries and especially immaturity of WebGL2 in those libraries, and modelling/art direction. The technology is pretty capable but the ecosystem around it pales in comparison to the platforms driving many of today's AAA and indie games.