Are you complaining that Google maps uses JavaScript?

No, Google Maps is actually a case where JavaScript makes sense. But this message reminded me of many seemingly static pages that are actually blank if you don't enable JavaScript, without even any hint that you should enable JavaScript. Reader mode often works perfectly on these pages. Sometimes, blocking the white element hiding the content of the page works well too.

I don't hate JavaScript, I have actually developed several web applications using it, and like it.

I'll complain that Firefox isn't supported.

Google is the worst.

It is though? I'm using it on Firefox without any issues

It's supported on Google Maps and not on Google Earth in the current version.

It's funny, but whatever remains should actually be html, css and images.

except for pages where all html and css is generated client-side by javascript.

we must be using different blockers, I see:

Aw snap! Google Earth isn't supported by your browser yet. Try this link in Chrome instead. If you don't have Chrome installed, download it here.

Or if you're feeling adventurous, you can preview a cross-browser beta of Earth built on WebAssembly.

I'm using uBlock Origin with JavaScript blocked by default. But your message is what I get on the Google Earth link, even with JavaScript enabled.