Because the market doesn’t deal with the news itself, it deals with its interpretation and outlook. At first, the news was understood positively: weak jobs means there’s a chance of interest-rate cuts, and that supports stocks. But after the first reaction, the market starts asking:
Is the weak data just a minor slowdown that opens the door to rate cuts? Or is it the beginning of a bigger problem in the economy and company earnings?
We also need to remember that markets often move before news. If investors had already been expecting the news and had bought it before it was released, the reaction can be the opposite—they may start selling for profit-taking. That’s why sometimes you see a strong bullish candle, followed by a quick drop—not because the news changed, but because the market’s interpretation of the news changed.