They seem to classify users in a way that puts technically-proficient users in a separate class to regular users.

One class receives a more traditional experience.

The other receives whatever they're currently pushing. For example, my Dad's Gmail has a much higher "ad email" : "real email" ratio than mine. Also, the styling of an "ad email" line is far more subtle than what I receive.

I checked with my technical friends. They all receive similar experiences to what I do. But my parents and other people I help with their personal tech receive the ad-heavy version.

My conspiracy theory is that they're trying to detect journalists, lawmakers, regulators, and more, in an attempt to avoid being forced to push ads less aggressively.