No, it's not that. It's that often, to make a new product you have to have multiple parts of the business work together. Then you will find yourself working with the other department and they'll frustrate you.
Some places attempt to solve this by saying that you can use whatever vendors you need to solve the problem but often the best place to solve it is the other department since the solution is infeasible without them.
The problem is that often the solution is infeasible with them because the guys who made them good have left and now you only have the lameos.
As to why they can't operate as independent business unit? Well, there's the Theory of the Firm to tell you why that doesn't work often.
Some places attempt to solve this by saying that you can use whatever vendors you need to solve the problem but often the best place to solve it is the other department since the solution is infeasible without them.
The problem is that often the solution is infeasible with them because the guys who made them good have left and now you only have the lameos.
As to why they can't operate as independent business unit? Well, there's the Theory of the Firm to tell you why that doesn't work often.