Direct answer: The market drop today was driven by a combination of continued weakness in high-valuation technology and AI-related stocks, concerns about near-term macro momentum (including delayed or incomplete economic data due to the earlier government shutdown), and a shift in investor sentiment toward higher-quality or lower-valuation names. Overnight and intraday moves often reflected a rotation away from tech into more defensive or value areas as yields fluctuated and traders weighed the potential for a slower near-term growth path and uncertain Fed policy signals. In short, tech-led selling, data delays, and rate expectations contributed to the broader market decline today.