Why do you think they aren't?

They're doing complicated things, but is that headcount in proportion to it? For comparison, Apple's HQ headcount is under 20k, and entire state level governments for small to mid-sized states are in the low tens of thousands of employees. We all know human things generate lots of work to employ lots of people, but the scale still feels a bit off, even if no one can point to exactly why.

It doesn't feel off to me. As others have discussed in considerable detail, operating in a lot of countries worldwide is a lot more complex than it intuitively seems to be, and the complexity scales superlinearly.

I suspect they might be a few percent overstaffed, but I don't think that hurts a company focusing on growth over all else, and I don't think it's even all that uncommon for such companies. It wouldn't surprise me to see a round or two of layoffs once that growth tops out, but it would surprise me if they added up to more than 10% of headcount.