Because it can’t actually be predicted or they would do just that.
Stocks aren’t necessarily an indicator of economic strength. The S&P 500 is in an earnings recession right now, but continues trading at all-time highs. The market can stay irrational longer than you can stay liquid.
Your chart is earnings per share, it’s also from June. That has increased because of all the stock buybacks following the new tax law. Total earnings are down.