This was mainly in large companies where departments are quite large and the regular workers don't really see what's going on. I have seen people in one department being told to keep working on their current stuff while new people were hired for the new tech. Once the new people were up to speed the old department was laid off. There was no effort to get current employees involved.
When do you suggest that they find time to 'study up'? Most corporate environments in which I have worked have an assignment:time ratio greater than 1:1. Often there wasn't an opportunity to take the legal statutory lunch break nevermind study.
Consider our industries project failure rate. I've been on projects where it was the new team on the new tech stack that's let go and the guys maintaining the 20 year old system get a huge boost to their negotiating power.
