The biggest competitor to Unreal engine, Unity, once had ~8000 employees. And Unity doesn't even make games.

(Not saying this is justified, of course. I think Unity is pretty much doomed.)

Don't make games, but Unity does operate worldwide and has a LOT of supports for ads (their main money maker, unless something recent happened).

That globalization is a big reason many tech companies swell. When you need a team to work in and around every region's laws and regulations, you get big quickly.

But also, unity has slimmed down and scaled down on a lot of initiatives.