There are some very big businesses using them. RB (a $20 Billion conglomerate) uses Shopify. And a large supermarket chain I know uses WooCommerce. From BigCo

There are some very big businesses using them. RB (a $20 Billion conglomerate) uses Shopify. And a large supermarket chain I know uses WooCommerce. From BigCommerce's S-1 filing, plenty of large companies use them. A company like Nvidia, while it has a $300 billion market cap, likely doesn't sell in massive volumes to consumers. More of their business is to OEMs.