Why did the transition to a productive mode of economy take place?

The Ice Age ended about 12 thousand years ago. Mammoths, rhinos and other large animals that were hunted by ancient people became extinct. It has become much more difficult to hunt smaller and faster animals with a spear. Therefore, people invented a new weapon – the bow and arrow. Rafts and boats appeared. Fishing nets began to be used.
Around the same time, people discovered that if they sow seeds of wild-growing cereals, then after a while it would be possible to harvest the grains.