There really wasn't any such thing as a tech stack - our company would produce software for various Unixen and, especially, Vax, and the language was alway C, with some Pascal on the Vax side (as, I was told, the Vax Pascal compiler produced far more optimal code than the C compiler).
Being a software engineer was like being a furniture-maker. You had to master a small number of tools - the saw, the chisel - and then craftsmanship consisted of discovering an affinity with these tools and a love of getting ever more skilled at using them. This path wasn't for everyone, which was fine - plenty of management and other non-tech roles for those folks - but if you grooved with your tools it was a real joy to be able to move from chair- to table- to cabinet-making and carry and refine your skills as you went.
This idyll could not last, however. Before too long it became uneconomical to make furniture this way, so for your chair making project you instead had to learn how to run a chair-making machine. When you moved onto a tables project, the machines there were infuriatingly dissimilar to the chair-making ones you'd just mastered. Worse still, moving back to chair-making after a year or two, you discover that the old machines you knew are now obsolete and you have to re-learn how to run their replacements. This stops being fun, or interesting, after a while, and yet sadly it's all that most younger software engineers know.
Occasionally, there is the need to make some shim or gizmo that the machines don't cover, so out come the trusty saw and chisel of yore - much to the amazement of the young'uns, who are astonished that an old-timer can still wield these antiques so effectively.