From that perspective, the stock market should have no volatility in share prices whatsoever - it should fairly value each company based on their profits over the next 15 to 20 years, and since those profits don't change, neither should the share price.
Stocks are based on expectations of future profits, i.e. psychology. "In the long run, the stock market is a weighing machine. In the short run, it's a voting machine."
Few investors' psychology will let them look at a year of bad news and still think "Oh, it's going to get better in the future." After about 3 months you start doubting yourself and wondering if maybe you were wrong in the first place, and you've entered a brave new world where people randomly die and commerce or long-term plans are impossible. All of the economic data - corporate earnings, employment, share prices, etc. - will reflect the new normal, so there's no reason (other than your memory of what the '10s were like) to believe that share prices would always go up.