It might just be me, but that actually seems pretty reasonable.
What I've seen a lot is companies, during growth, accepting less-than-ideal candidates, maybe without a good onboarding, which then end up as deadweight in the worst case, and underperformers in the best case.
This, combined with a tendency to keep people around who have been there a long time, and the people themselves knowing they're not going to be let go, could result in massive companies and hundreds of people per product.
Yes steam is big, but it's not a product so complex you'd need over 100 people to maintain it. I assume other companies need so many people because tasks don't get done, and the logical step is to add people, not remove people.
Staying lean means staying agile (in some definition of the word), and that can speed you up.