There is a very clear use case in the first sentence of their comment though?

Unless your stance is that WebGL itself had no real use case, which is just silly.

Why does a web page need GL?

I don't know, ask any online maps site.

Or, say, literally any number of e-commerce sites that give the user an interactive and/or customisable view of products and not just static imagery.

Or, say, any number of pages that embed complex data visualisations.

"Why does a graphical UI platform need performant graphics" is an incredibly tautological question.