Why is there no grace period of one to two minutes?

In Switzerland, the requirement is that a valid ticket must exist for a journey. Accordingly, passengers should also be able to rely on a uniform, nationwide and comprehensible regulation. In return, however, this rule must also work in all public transport systems (local, regional and long-distance), especially in local transport, where the journey time between two stops is often only a few minutes or even seconds. What's more, the same discussion would arise with a grace period; simply one or two minutes later.