Several reasons for not switching back, some idiosyncratic:

* I trust Chrome more than Firefox on security

* I'm used to Chrome's debugging tools, and would need to learn Firefox's

* I use the Chrome password manager, and it would be annoying to switch

If Firefox were enough better I would still switch, but at this point my understanding is it's more like "Firefox is no longer slower than Chrome" not "Firefox is a step up from Chrome in the way Chrome once was from Firefox".

That's understandable though I imagine it's unlikely we'll see something like that ever again, right? To me it seems kinda like how race car engineers used to be able to discover some major advancement in their engines that would give them wins for a few years but nowadays it's much more homogenous and worked upon for much less significant gain. I don't know much about the deeper webdev stuff though so who knows, but it seems like that could only ever really possible with a shift in a browser trying some novel shift in architecture.