The problem is that developers have a very strong incentive to add new technology to their resume, as their job is not guaranteed. I think most junior devs have

The problem is that developers have a very strong incentive to add new technology to their resume, as their job is not guaranteed. I think most junior devs have seen some old hat at their first real job who codes in one, ancient tech stack; someone that they perceive as un-hirable if the economy takes a turn. We all see the job listings out there and the tech they desire. It is self-preservation, and it is in direct conflict with what is best for the company itself. To use myself as an example: I have zero regrets with pushing for JavaScript over VBScript many years back, for moving from Microsoft HTA to React, or for moving from Yahoo's YUI to jQuery. Being infused with old tech can very severely limit your ability to survive. Most of my interviews after my first job were simply explaining/defending the ancient tech I had specialized in. It is all risk, no reward at the employee level.