These crossovers are widely reported because they are simple and slow. A golden cross says the intermediate trend has turned up relative to the long-term trend; a death cross says the opposite.
They lag badly. By the time a death cross prints, the market has often already fallen a long way, and it sometimes marks the low rather than the start of a decline.
Example: the S&P 500 printed a death cross in March 2022 near 4,300 and continued to 3,500 by October; it printed one in March 2020 near 2,700 within days of the low.
Related: moving-average, trend, index