Why did Delilah betray Samson?

Answer 1

Delilah was a Philistine. Samson was a Jew. At the time, the Philistines had control over much of the Jewish lands. Samson had started a one-man attack on the Philistine overlords and this was not appreciated by them. Oddly enough, however, Samson had a weakness for Philistine women. Delilah had the opportunity and the motive (protect her people) and she took advantage of that. The Philistines have long since disappeared as a people.

Answer 2

Delilah was approached by the Philistines to do so. In the absence of samson's strength, would make the Israelites weaker.