Rewriting existing code in a new shiny language just to keep employees happy is a pretty stupid thing, sure. But when you're just solving problems and maintaining old software, there's a lot to be gained from thoughtful, measured inclusion of new tech, transition to new libraries and such. This is technical investment in the company's future: improving developer's velocity and code's performance, reduce bug rate and overall quality of the software.
At least in my personal experience: moving from SVN to git, moving development from C++ to JS (and company was making simple mobile games that are never CPU-bound) and then gradually adopting Typescript, migrating a commercial application from MSSQL to Postgres (saving a significant amount of $$ in license while actually improving performance), and many, many smaller refactorings, improvements and new shiny libraries — all resulted in direct positive consequences for the business.
If the company never adopts any new tech ever, it's a sign that it's lost its way.
There is something called tech debt and I can understand it but just replacing a Bootstrap/jQuery based app wit React/VUE just because it is new does not make sense. I will not mind upgrading from Python 2x to Python 3x but I will always resist to replace Flask with Django, unless there is some really genuine reason behind it.
At least in my personal experience: moving from SVN to git, moving development from C++ to JS (and company was making simple mobile games that are never CPU-bound) and then gradually adopting Typescript, migrating a commercial application from MSSQL to Postgres (saving a significant amount of $$ in license while actually improving performance), and many, many smaller refactorings, improvements and new shiny libraries — all resulted in direct positive consequences for the business.
If the company never adopts any new tech ever, it's a sign that it's lost its way.