Let's say you have one profit bringing business unit like google ads. (Let's call it main unit) but you also have internal startups in your company (side units). But you only have one operations department, only one HR department etc. How do you account the expenses of these departments in relation to main business and the side units?
You can't. If people are not forced don't write down exactly whether they spent their time on working for the main unit or the side units units, you can't later account it correctly. Unfortunately it's not even clear for the company what happens sometimes. You might for example hire an employee, but place him in a different business unit than originally planned. Or the employee later on changes business units.
The other problem with this is even if you require such a strict accounting setup, you can't tell whether employees and/or departments are accounting their efforts correctly, it's just incredible difficult to enforce the rule; to make sure they don't lie.
Even if you think hey you can do it, you have to rigorously enforce this for all companies in your juridiction, because as soon as you stop looking, they will stop caring.
So the problem is you can't tell the profits before "internal investments" as long as you can't pin down operational costs.
You'll see that the only thing that you can accurately account for is the main business units revenue, but you can't give a precise number on operational income. (Which is revenue - product costs - operational costs).
