Isentropic means there's no effects from friction, boundary layer, or turbulence. Airflow through a fixed duct is mostly isentropic, airflow through a duct with a changing wall IE the floor of a car and the road, the flow is NOT isentropic, thus isentropic assumptions are not correct. The road surface is rough textured and the sun shining on it creates a boundary layer of air over the road. All of these factors increase the turbulence the air experiences in the duct. Furthermore the turbulence of the tire is added to this turbulence.

To summarize

https://files.catbox.moe/5679d4.jpg

If the downstream pressure is approximately half of the upstream pressure, we achieve choked flow at the throat of any duct. When this happens, the pressure downstream drops, just like sand passing through an hourglass. This is because the air gets choked by the supersonic shockwave that occurs just after the throat.

There are two ways to create this pressure imbalance, we either increase the reservoir pressure stagnation pressure, or we lower the downstream back pressure. Or the two combined.

This law comes into play with the new F1 cars which are essentially ground effect cars, with two huge venturi tunnels. The goal becomes two fold, create choked flow at the inlet of the tunnels, and create two strong vortices to lower the pressure behind the throat of the tunnel.