What stops the spit getting to the other headland?

The spit doesn't reach the other headland primarily due to wave action and longshore drift. As waves approach the shore at an angle, they transport sand along the coastline, forming the spit. However, the energy of the waves diminishes as they encounter the headland, preventing further accumulation of sediment and allowing for the formation of the spit while leaving a gap between it and the headland. Additionally, the water depth and currents can also influence sediment deposition and transport.