Answer:
They needed more reliable sources of food and supplies.
Step-by-step explanation:
The Hilly Flanks hypothesis, proposed by Robert Braidwood in 1948, suggests that agriculture began in the hilly flanks of the Taurus and Zagros mountains, where the climate was not drier as Childe had believed, and fertile land supported a variety of plants and animals amenable to domestication.
Quoted by: Wikipedia.