I just can't understand why the stock market keeps going up.
Interest rates are negative. This causes people to chase and a big factor in this bubble. Companies are borrowing billions for free to do stock buybacks and keep the price going straight up. Nothing lasts forever. When is the big question.
What does happen, however, is that many modern buyback deals include a bid that gets more aggressive as the stock trades down. So in a selloff, the buyback actually supports the stock more than in a rally. This reduces downside volatility and prevents panic.
The debt problem is a huge issue, but with interest rates as low as they are, it's not entirely crazy to say "we think we will return more in capital gains from buying our own stock than we will be charged in interest for the loan to do so."