Because of the scale: ALPR’s track where everyone is and was all the time. This allows entire categories of intimate information to be learned, that clearly threaten the civil liberties that the 4th amendment was written to protect.

For example, an officer sitting on a city street is very unlikely to learn where his wife goes every day, an ALPR search will answer that question.

An officer walking along the street making note of what he sees is very unlikely to observe and make note of the precise daily movements of someone in August three years ago, an ALPR search will answer that question.

The degree/kind distinction you’re aiming at is meaningless, it’s like trying to argue that shooting someone with a firearm is the same as shooting someone with a paintball gun in principle, sure but maybe one of them is orders of magnitudes morw powerful and impactful, and so deserves a different degree of consideration in how and when it is applied?