First lack of budget to keep them there full time, then they'll re-skill and change industries due to lack of job opportunities. Sooner or later they won't be able to easily go back, because tools, styles, and publisher and reader tastes change, as well

If you spend a decade or three learning and perfecting your trade, and spend a decade away from it without practicing, you'll be rusty (at best) regardless of what the job actually is

This fuels everything from shipbuilding to the military industrial complex - you practice and improve by constantly doing and refining, and your nation can end up a world-leader in designing microprocessors or building supersonic fighters