True. Though, if you prefer to play scenarios as I do, you are stuck with what the designer gives you. I am playing one of the Kriegsburg battles at the moment. 2 hrs duration, big map, lots of artillery assets and no TRP's. I would say that is more often the case than not.
Of course, scenario designers could add more TRP's, but a few extra options for time delay would be a more generic solution.
I was more just curious to know the 'why' of this limitation rather than expecting a fix.