It's not only for Vezel but valid for all cars that have not been sufficiently used for some time. All fluids have a life and start oxidising specially if they are stagnant. So the fluid being new looking and clean is not the only criteria. A car that is regularly used keeps flowing those fluids through its system thus keeping it intact. Whereas a car that is not being used obviously the fluids are still and start losing their ideal viscosity. This is not just for Engine Oil but also for almost all fluids such as transmission oils, brake oils, coolants etc to be on a safe side. For example ever observed leaving a container of water still for some days? It starts getting contaminated by itself.
These are the exact reasons why all car service manuals have a description such as "5000kms OR 3 months". We usually ignore the time/month part and only focus on the kilometres part which technically is wrong. Specifically wrong even more for cars not being used