Because they were enticed by the idea 'they would be like God' Not that ' they would know right from wrong' When in fact they already were ' like god' because they were made from him They had a personal relationship with him. Walked with him. That was the only thing besides multiply and keep upbthe Garden they were asked to do. The issue is disobediance wether they knew right from wrong or not. They were told not to touch it.