my personal theory is that it's intended for the ground/power (left/right/center) to make contact first, and for the other pins (with the thin strips) to not make contact with the pins until later
so why keep the thin strip? factory testing! before the board had been cut off to make the card edge connector, it was connected to something else (a row of testpoints?) for factory testing or programming, since nobody wants to insert each cartridge one by one