Yeah, we had been doing that initially and found that there are lots of imaginative ways to use e.g. refresh meta-tags that browsers do accept but we did not (e.g. somebody might say content="0.0; url=https://example.com/"*) and more and more networks and agencies switching to JS-based redirects lead to a headless browser being easier in the end, despite dealing with these specific issues.

A simple self.location.href = ...* is still doable (-ish, because I've seen conditional changes that were essentially if(false)... to disable a redirect, which we obviously didn't consider when pattern matching), but once they include e.g. jQuery (and some do on a simple redirect page) it got far too complicated.