Answer:
Because it allowed those cultures to had more terrain to farm and in that way be able to feed more people.
Step-by-step explanation:
Terrace farming is an agriculture technique that consists of creating flat surfaces or platforms similar to steps on hilly or mountainous terrain. By doing this they create more effective farming.
Because of the mountainous terrain in which the Andean cultures live this technique was very useful to them. It was first used by the Wari culture but the Incas improve it.
I hope this answer helps you.