A varnish cache won't help you if you're running something like a code forge where every commit has its own page - often more than one page, there's the page for the commit and then the page for "history from this commit" and a page for every one of the files that existed in the repo at the time of that commit...

Then a poorly written crawler shows up and requests 10,000s of pages that haven't been requested recently enough to be in your cache.

I had to add a Cloudflare Captcha to the /search/ page of my blog because of my faceted search engine - which produces may thousands of unique URLs when you consider tags and dates and pagination and sort-by settings.

And that's despite me serving ever page on my site through a 15 minute Cloudflare cache!

Static only works fine for sites that have a limited number of pages. It doesn't work for sites that truly take advantage of the dynamic nature of the web.