I would say that Frontend development in general (HTML+CSS) and the whole javascript ecosystem are a nightmare of patches on top of other patches, and endless exceptions and small components whose sole job is to plug some hole from a different technology under it. You need endless people and bruteforce to build on it and provide more value for the end user. In comparison, Backend can turn bad sometimes, but a well de…
As a frontend dev there are definitely well designed frontends. I've seen a lot of bad backends too. It just depends on how much engineers are able to plan ahead and also keep tech debt under control.
A backend from a decade or two ago can still run fine, because it defines what it runs on. It doesn't matter if CentOS 5 deprecated a feature the apps needs, we can run it on a CentOS 4 VM (not that anyone should).
Frontend feels like it has more churn because it can't define it's own runtime. If Chrome deprecates a feature, frontends have to adapt to that. Because frontends have to adapt to their runtime changing, it becomes important to use a framework that's currently supported. You can't keep running on Java applets, because browsers won't run them anymore. You can't keep running on RandomJSFramework if it stops getting updates, because features may get deprecated in the browser.
I think it has less to do with the average frontend vs backend dev, and more to do with the environment they operate in.