Comment by LMYahooTFY

You're missing the economies of scale part.

OP is saying it's cheaper overall for a 10 million customer company to add infrastructure for 1 million more than it is for a 10,000 customer company to add infrastructure for 1000 more people.

If you're looking at this as a "share of the pie", it's probably not going to make sense. The industry is not zero sum.