The applicable condition of special relativity is the metric transformation between inertial systems. However, there is no real inertial system in the universe, and even if there is a system with uniform linear motion, it cannot be really observed.
In the above figure, A is a stationary point relative to the paper or screen, and B is a system that moves linearly with speed v relative to the paper or screen. But in A, the ratio of its distance to time is not constant, so it is still not an inertial system.
From the derivation process of Lorentz transformation and the prerequisite of Lorentz transformation, we can see that the applicable scale is infinitesimal and the time is infinitesimal. Mathematically, this is a differential conclusion.
General relativity is undoubtedly a macro-applicable theory, and the macro result must be the cumulative result of countless differential points, so it is an integral expression of relativity.