Unprecedented low interest rates (access to cheap cash, lower debt servicing rates, poor returns on bonds), trillions of dollars of stimulus spread liberally around the world, and signs if significant pent up COVID-induced demand all point to a massive rally in the short term. There’s just no other place for investors (institutional and individual) to put money and receive any appreciable return. Take advantage of as much of that as you can.
I’m not saying asset values will defy gravity forever, and I’m not saying P/E ratios no longer matter, but this rocket had been fully fueled and the fuse has been lit. It may very well end in a spectacularly destructive explosion, but I’m guessing not in 2021.