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 product

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.