Prince Rupert's Drop vs. Hydraulic Press
The way the drops are formed involves the outer layer solidifying quickly and the interior slowly cooling.
This causes the molecules of the glass to contract enough that basically every molecule of the drops' head is constantly pulling on all the other molecules, and this force needs to be overcome before any part of the drop will break away from the rest.
So instead of needing a small amount of force to crack or chip the glass, it basically takes as much force to disintegrate the entire thing at once to break it even a little.