In a perfect world for investing you would be able to forecast the future cash flows for any given company with 100% accuracy. By knowing that number you would be able to pay a perfect valuation for that company.
There are forecasting models at every brokerage office in the world, but like your 5th-grade math teacher said: “garbage in, garbage out”. If you get the future cash flow wrong, then your target price will be wrong.
So, the short answer is, that the market has a ton of companies that are priced as if the free money, zero interest rate, strong employment, and low inflation rates were going to continue forever.