A big reason why technology-heavy Nasdaq Composite COMP, -1.47% is dropping 1.5% in afternoon trading Thursday while the Dow Jones Industrial Average DJIA, +0.89% is rallying 292 points, or 0.9%, is the bad performance of the shares of the four biggest tech names. Of the four U.S. companies with market capitalizations of over $1 trillion, shares of Apple Inc. AAPL, -3.14% dropped 3.1%, Microsoft Corp. MSFT, -1.98% slid 1.9%, Alphabet Inc. GOOGL, -2.80% GOOG, -2.37% sank 2.9% and Amazon.com Inc. AMZN, -3.73% slid 4.1%.