Being "stationary" works for **models**, and that's why we say what we say about relative motion.
But our models aren't reality. We may perceive something to be stationary, and we may make scientific, mathematical, and geometric models of that thing in which we show that it is stationary, but such models (as well as our perception) may not always be accurate.
Just as in the example above where the two cars **seemed** to be stationary from a certain frame of reference, a different perspective might more closely resemble reality.
It brings home the bacon. Maybe bacon isn't reality either.