Answer:
Because things evolve fast
Explanation:
Professionals in the computer industry need to be constantly learning and adapting (by continuous education and by self-learning) to the new technologies appearing on the market, learn the new programming languages rising in popularity and so on.
If they don't, they'll end up with skills that are outdated and no longer in demand in the work market, so they will have a hard time finding work to earn their living.
