Big Tech stocks have been underperforming for months due to concerns about ballooning spending on artificial intelligence and a rotation into sectors that tend to do well in an expanding economy. Nvidia Corp. is priced at a little more than 21 times forward earnings, which is basically the same as the S&P 500 and down from its 10-year average of 35 times. Amazon.com Inc. shares are priced at 23 times forward earnings, half their average multiple over the past decade of 46.