To counter your experience, mine (in London) was almost exactly what Animats described. I worked on the same application for a decade, we introduced new tech when appropriate, but we also stuck with the fundamentals we chose right at the start simply because they weren't broken. That did mean, however, that when I came to looking for a new role I was _way_ behind other candidates.
Adding my anecdata for London, yeah, if you haven't been tracking the bleeding edge of JS framework and node insanities, people will mark you down because everyone* is looking for "full stack devs".
* Unless you want to do Perl maintenance or C++ for fintech, I suppose.
