I think investors are fully invested. I am. What else can we do? It's just the companies aren't translating that into increasing productivity. There is less R&D, fewer new production facilities opening (even in China), barely any wage growth (stagnant consumer spending, catch 22 right there), keeping old machinery rather than replacing with more efficient machinery, little product innovation, I haven't seen anyone expanding into foreign markets (quite the opposite), etc. It's as if everyone looked around at everyone else, collectively shrugged their shoulders, and said "I dunno".
What companies ARE doing is borrowing at really low interest rates and buying back shares. There are multiple reasons for that. It's a cheap shot at raising share prices. By buying on the open market there is one more bidder nudging the share price ever so slightly higher, and reducing the number of shares that can be sold. It also reduces the number of shares, thereby artificially raising earnings per share. Remember, many CEOs are partially paid in stock options, so they benefit directly from higher share prices. They were supposed to do that by improving market share, revenue, margins, etc, but they just found the path of least resistance instead. I don't know how to fix everything else, but CEO stock options and share buy backs should be mutually exclusive at the very least. Heck, pay it back as a special dividend and let me decide if I want to buy more shares or spend that money.
Inflation might work. Japan is trying that after decades of mediocre growth. Doing so by raising interest rates risks stalling what little progress there has been though. If the fed does do that then they should have started a year ago, because the higher markets go, the further they fall.