For a UI framework landing page, this looks impressively bad on mobile.

Big Arial at random sizes. No margins, no grid, component examples scattered all over the screen.

This was my first impression as well. The layout options just didn’t work on mobile

Welcome to the future! We better get used to it.

Are you being a troll, or is there a trend afoot to ignore mobile rendering?

It is a shallow trend to ignore or on-purpose worsen mobile experience and force users to mobile apps instead of using the browser version.

Though I'm not sure if this can be applied in this specific case.

The trend is people releasing barely conceived software and products written by language models, backed by equally thoughtless marketing materials written by language models.