At the end of the day, some people like Javascrip and CSS. And "full stack" only means that they will work with those, SQL, and some backend language (that may be Javascript too). It doesn't imply anything on the workload, all it does imply is that the place is hiring a generalist instead of specialists.
The last job offer that made me smile was for an AI / fullstack developper.
Aka the platypus of software dev.
The problem is pretty simple.
Let's say you are cutting-edge in all the technologies that make you very adaptable at time T.
You get hired.
You decide a stack A/B/C/... for your next project.
You get stuck in that project for ... let's say 3 years.
(a reasonable time for a project to reach production and have a few real-life iterations).
If you are not an assh... who leaves after 2 years (leaving the production/maintenance to others, i.e never having lived the "hell" of maintaining things for real), then you are 3 years-behind in all the technologies that are not in the A/B/C/... stack.
Now, at time T+3, you are ... the obsolete man [for TTZ fans only :)]
Frontend has very few to do with HTML and CSS nowadays.
It all has to do with framework choice, the build toolchain, the unit-testing of the front, the server-side rendering vs the client-side, the architectural layers (or bricks) to use on the client-side, SEO, performance, CI/CD, browser compatibility, components lifecycle (yumm, library versions upgrade!).
At the end of the day, some people like Javascrip and CSS. And "full stack" only means that they will work with those, SQL, and some backend language (that may be Javascript too). It doesn't imply anything on the workload, all it does imply is that the place is hiring a generalist instead of specialists.