There is a reason a month figure is written in the change oil interval time frame. Oil degrades over time whether it is driven or not. Once ran in the engine the oil has to deal with contamination, combustion byproducts and moisture. All of these deplete the additives in the oil over time. Oil ran for 5000km and 3months is still probably in better shape than oil sitting in an engine (not being run) for 2 years.
An eg of a vacuum tight system would be brake fluid. It does not have other contaminates entering like engine oil does. But it still has to be changed eventually as the chemical properties degrade over time.
Better quality oil will last longer (time and km wise). OP, you dont have to stick to 3months on the dot as one can be more flexible towards the month counter. But dont assume that you can keep it for long durations despite not driving that much.