The general idea is that while there are a lot more small businesses than large corporations ( 72% vs 20%), corporations still make the vast majority of sales. You could discuss why you think this is, what the differences between small and large businesses are, and why there is such an inverse relationship between market share and total receipts (aka sales).
One reason is that while there are a lot more small businesses, each only sells a very small amount whereas a single large business can sell much more because they have better websites, more stores, etc. Think about local restaurants vs Mcdonalds. There may be 5 local restaurants for every 1 McDonalds in your city, but McDonalds still sells way more food than all of them combined.