I wish I could find the picture that someone posted of a dissected Wago or Ideal Push-in.
It may not have even been on this forum. But it was as Don said, more surface area and also the clamp/spring looked to be some type of gripper also.
To add to why these are different than back stabbed devices, the back stabbed devices are subject to repeated pushing-pulling-flipping on/off. This can loosen the clamp after a while, especially if they weren't inserted fully to begin with.
The Wago type connectors are used in place of wire nuts. They don't go directly on a device and thus are not subject to the same potential movement of a receptacle or switch.