Being in demand means close to nothing. Once I was contacted to work on a tool that was developed in Delphi and I would hardly suggest anyone should pivot from their career to jump on that gravy train.
You should build up the skills required for your next job, not your current offers.
If the price of a stock or house or investment have been rising for two years, it's risen in cost to get into, and you might never see the gains people have seen in the past; I doubt you'll ever get a bitcoin for a dollar again!
But if job adverts for a new tech have been rising for two years, it doesn't cost any more to learn than on the day it was released. Maybe less, in fact, as there will be more tutorials and more experts to learn from.
Kubernetes is pretty lean. It does require a significant mental load to get up and running, but that's mostly due to how it forces developers to venture into the old and largely unfamiliar sysadmin territory, where you need to pay attention to more stuff other than the compiler finishing a build job.
I don't need to spend my time developing skills for the job I've already got, I need to develop skills for the next job I'll have
> most businesses don't even have a compelling reason to switch from the old 3 tier monolith architecture.
...thus showing I can't rely on my employer to keep my skills up to date for me.
Not that there's no market for specialists in older technology - back in 1999 I heard rumours that COBOL experts were commanding huge salaries to work on millennium bug mitigation in banks. But people following that career path should be choosing it consciously, not by accident :)