It is insane. And it is entirely fueled by access to cheap money. Rates for the past decade has been near 1% and only recently started climbing but still below 2%.

I can't speak for Apple et al but for some companies it has been a tool to raise their share price. With shrinking outstanding number of shares financial ratios like EPS etc start to look big even when the company isn't actually growing. And that means over time these companies can borrow even more money on their "growth". The cycle repeats.