There are checkpoints, they are (usually) manned and funnel traffic through single lanes, it's just that they rarely actually stop people.

That's how they work. I was stopped at one of those between France and Switzerland.

Stopped, searched (me, my gf at that time and the car) and drug-tested.

That's the point. They do check quite a lot of people for undeclared goods. However they're no after those who buy stuff for themselves, but for example restaurant owners who try to smuggle in cheap meat in big quantities.