Because their biggest buyer(s) just ran into a buzzsaw. NVDA's stratospheric valuation is based on a few select customer's unrestrained ability to purchase the latest products. That unrestrained spending ability was fueled by the "AI" arms race. If those companies see their ability to be profitable with "AI" as diminished then their ability to continue spending with NVDA is probably going to be diminished as well. Anything considered bad for NVDA's top spenders is going to be viewed as bad for NVDA as well.