Yes, something feels off. My guess is that huge funds and algo traders have found that the optimal strategy is to create massive long positions while there aren't any major crises. I bet someone out there knows what will trigger a reversal of this strategy-- after all, the gains are only real if you lock them in by selling.
If we continue to make holding cash unprofitable, those who earn money will invest in equities. The length of our current economic cycle is inversely correlated with GDP growth.