It kinda goes the other way too though, no? A business generating $1 billion in revenue might have 10k employees. A smaller company doing $10 million in revenue might have 100. The commensurate value of a given employee is not that different.

And the number of employees also affects the types of efficiencies you can introduce; the likelihood of finding something that will increase revenue at a higher percentage for a large company is drastically lower than the likelihood of finding something that will increase revenue at a higher percentage for a small company. And that's if it's percentage based in the first place, rather than fixed savings.

Anyway, relatedly, it has more to do with the fact that a lot of the leading tech companies have a high amount of revenue -per employee-. That is, revenue/employee = big number. There's a few different reasons for that, but that's the main thing. Per the example above, it's really more like a company doing $1 billion in revenue has 10k employees, and another doing $100 million has 5k employees. Obviously the former has more to spend on employees, as they're generating more with fewer.