They don't have anywhere near close to 51% of American commerce. * Total US Retail sales in 2018: ~$5.4 Trillion * Amazon trailing 12 months revenue as of Jun

They don't have anywhere near close to 51% of American commerce. * Total US Retail sales in 2018: ~$5.4 Trillion * Amazon trailing 12 months revenue as of June 30, 2018: $208B. This is a little less than 4% (and that's assuming all Amazon revenue is US-based and retail sales, rather than AWS or other...) You may be thinking of share of growth of US eCommerce.