They have ~5000 employees.
Most game companies are a tiny fraction of that size. Even most AAA games are made by teams of hundreds. Not teams of thousands.
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.)
Epic Games does way more than just purely making games.
They also have their own Steam competitor (Epic Games Store) and, more importantly, they develop and support Unreal Engine used by tons of other game dev companies.
If you want an apples to apples comparison (i.e., other big live-service game companies) in terms of the employee count, you got:
Mihoyo (Genshin Impact, Honkai Star Rail) - ~5,000-6,000
Riot Games (League of Legends, Valorant) - 4,500
Roblox - 3,500