AntiManutoo,
let's suppose I'd want to manage a 15-person team (spoiler alert: I don't

), this would take me so much time that I'd be barely able to work on the game. And I'm the only one on this planet to be able to bring the new stuff it needs. Even if I gave some of my simpler coding tasks to other people, it'd take them at least 10 times more time than me to do them, as they'd have to dig into unknown strange code.
Little notes :
- TE Physics isn't moddable
- I won't create any 3D content by myself, I'm not an artist ; even in TE3, I didn't create a single 3D object (IIRC) (I had to re-skin the 3D male player, though, coz the freelance who did it was a noob

) ; I only did the menus in 2D, and for TE4 a freelance already did the base menu design (unfortunately, it let me do the finishing and some more

)
- it's very complicated to find skilled people, it's a huge process in itself