Some parts deteriorate with age. Here in California sun and smog will rot rubber so replacing tires and drive belts due to age is wise maintenance but spark plugs don't age and now that we have unleaded gasoline they rarely need cleaning or replacing, only adjusting because the center electrode burns away.
Oil does get contaminated with condensation just sitting, although in a scooter not as much as in the large crankcase of a car so age is probably not a factor. I suspect the time issue is mostly for dealer profit.
I say inspect the components and use your judgement as to replacing them. Brake fluid does absorb water and replacing it every two years will prevent wheel/master cylinder corrosion but otherwise will not affect brake operation. I open the bleeder and pump/pour new fluid in via the reservoir, takes me less than 10 minutes per side. ABS bikes definitely should have brake fluid changed every two years.
I never replaced a wheel bearing on a two wheeler and I have gone at least 200K miles on my various motor bikes. Those are sealed, lubed roller bearings with little weight on them. If no side play, no notchiness, leave them be.