Not why it can’t be done so much as why it isn’t done. Share buybacks allow companies to reward executives directly as their compensation is tied to stock price. If we started not doing that, the priorities might shift, but those executives like things the way they are.
Before Tim Cook Apple had never done a buyback - Jobs was always thinking Apple could do better with the money in R&D than paying off shareholders. Wall Street did not approve of this position, but Jobs wasn’t one to listen to anybody, so it did not matter. Most CEOs are not going to take such a strong position when they, the stockholders, and every other executive can be guaranteed a financial reward through a buyback.
Before Tim Cook Apple had never done a buyback - Jobs was always thinking Apple could do better with the money in R&D than paying off shareholders. Wall Street did not approve of this position, but Jobs wasn’t one to listen to anybody, so it did not matter. Most CEOs are not going to take such a strong position when they, the stockholders, and every other executive can be guaranteed a financial reward through a buyback.