There are also cases where small teams that have grown grow unproportionally to the size of the product, and while the product is set up in a fairly sane way (and there is little wrong with it!) having 20 fresh people swarm into it destroys both the architecture and the execution. And with a small team enforcing cohesion for both of these is much easier! So a small project might as well stay small, but this should be somewhat a priority.
Mythical man month in action.