Another problem is that developers will start pushing for solutions in their current job not because it makes sense but because they know they're going to need

Another problem is that developers will start pushing for solutions in their current job not because it makes sense but because they know they're going to need those skills in their resume in a year or two. The company is left with a React-sized hole (or k8s, or Vue, or whatever) when the developer moves on that they need to fill ASAP, and the cycle continues.