At the risk of sounding obvious, simple programs are simple to create whereas complex programs are exponentially more complex to create. Add in more people with more complex communication paths amongst the team and your complexity may easily transcend what's feasible. The biggest problem is inexperienced developers and project managers can't recognize the complexity spiraling out of control beforehand but rest assured when it happens the coding is not "fun"!
> It’s better to admit that coding is complicated, technically and ethically.