Being a programmer, you should know they don’t hand write all the code, let alone every character. Tons of those “millions of lines of code” are reused libraries, many of which Asobo didn’t write at all.
Hand written by someone sure, but years ago, for a different project, by a different team, then reused where appropriate.
If you didn’t know that, it’s an important lesson to learn as you start your journey into development. Never reinvent the wheel when you can copy/paste work that’s already been done and adapt it to suit your project’s needs.