The cultivator is a gate to keep you from having better foods immediately. Later you will find more gates on producing good food -- the fishing rod, the spice rack, and so on. Just like getting the next tier of weapon takes some work, so does the next tier of food.

Reality, yes, you can plant a seed with a hoe. But to properly tend a good sized garden capable of feeding a family, you need more tools than just a crude hand made hoe. Raising one pet carrot in a pot is easy. Raising enough to eat all winter is a lot of hard work and additional tools make it much easier.