Sure, in PHP, the reality is that after your request is processed, all the state is garbage and is thrown out. But once you embrace that reality and stop trying to make sculpture from garbage, you can make some pretty damn fast pages that get straight to the point. Of course, a lot of people look at my fast PHP and say that it too is garbage, but at least it's fast garbage :P
That being said there are very decent options for long running processes/application servers these days - see RoadRunner, Swoole and Frankenphp.
Where "application" is basically a single page with less code than a typical React page. Even 20 years ago you'd run into DB struggling to give you data fast enough before you hit any issues with the "re-running the entire app".
And you have to screw your database really badly to see any issues early. Hell, phpBB was horrendously bad, running dozens of heavy DB queries on each page, and was still powering some of the internet's busiest forums.
> Now there are a whole bunch of tricks both in the language and with tooling to alleviate that, but still it's inherently there. It's an advantage for other reasons though.
Yes. It is an enormous advantage: it's fire and forget. You don't need to "SSR" your app (getting all data and state), ship it to the client with a bundle, then "re-hydrate" it (once again pulling data and state from the server) etc.