Comment by danielrhodes

None of this should be particularly surprising: if you choose to be complacent in your career you can't expect stability or increased prosperity over the long term. The path from a junior engineer to a lead engineer is quite short relative to a your typical career length. If you don't wish to move into management or elsewhere, there isn't anywhere else for you to go except laterally. After a certain point the impact of a person's improved programming skills does not get significantly better over time, at least for what most companies need. Therefore a company becomes incentivized to hire younger engineers who cost less as they still get similar or even better output.