I agree and sympathize with this, and it doesn't just apply to web development. My experience so far has taught me that it's probably best to get a hello world-level understanding of some options, pick what resonates with you the most and stick with it, until your employer tells you otherwise or you get bored enough to start learning something new.

It's often better to expand your skill set than moving on to a new employer to work with what you have already mastered. Most likely you'd be better of as an all around web developer in fifteen years than, for example, as a Vue specialist. You'd be maintaining legacy apps until retirement after your primary tech goes obsolete... There are thousands of people still maintaining Perl/CGI apps today, and I doubt they still feel inspired.