Plus they've had a very long time to grow their teams. Skyrim came out 12 years ago. We're looking at over 15 years delay for a sequel to one of the best selling games of all time.
On the short term, you can't grow very fast. Developers take a long time to onboard and while new ones are onboarding, senior devs will have to spend a bunch of time mentoring the new ones. But on the long run, you can certainly scale up considerably, especially with enough investment.