Why is security screening done at the gate in some airports?

I've noticed that when taking non-Schengen flights at AMS (Schiphol airport, Amsterdam), there is no centralized security check after you enter the airport and go through passport control. Instead, the security check happens right at the gate. The security checkpoint opens about an hour before the flight departs from that gate. This system seems to have a huge number of disadvantages:

• It must be really expensive - there's an X-ray machine, metal detectors, and for some gates even millimeter wave scanners at each gate.
• Also, adding to the expense, there are washrooms at each gate, since passengers can no longer use the common area washrooms after passing through security.
• It's really inconvenient for the passengers. There's no way to reach the seats inside the gate area before the security checkpoint opens, so people are forced to either wait far away in other areas of the airport, or (as I've seen many people do) sit on the floor, which is especially a problem for the elderly, etc.
• The security lineup tends to be very long, since all of a sudden an entire plane-full of people tries to pass through a checkpoint with very limited equipment (i.e. usually just 1 x-ray machine)
• Once inside the area, it's essentially an entire plane-full of people in a small area with no way to spread out, so there's always a shortage of seats
• There's no way to buy e.g. a bottle of water (not to mention duty-free alcohol) in the secure area of the airport and bring it onto the plane, something that is generally allowed in typical airports
• Security screening personnel must roam around the airport from gate to gate

I can think of only one advantage of this system: Arriving flights from non-Schengen countries (whose passengers must be re-screened for security) can just let people out of the plane through the gate - there's no need to "route" them through the secure area to a non-secure area, since everything is essentially a non-secure area. But surely this could have been solved at the airport design stage, as it is solved in many airports worldwide? Is this just a design oversight or a conscious decision? Are there other reasons to use such a system that I'm not thinking of? Is this typical in other European airports?