If I have a household robot that can plant a garden outside my home, why wouldn't I sell its services so that it also worked at a larger fully-automated municipal farm that could allow for a much larger surplus of food?
It would probably be more cost-efficient for the large farm to rent larger, more expensive farming robots from big companies, or to buy them. If you only have a 1/4 acre yard, obviously a smaller, cheaper robot will be the best option for you if you want to create a garden. That type of machine will be suboptimal for a large farm.
It would make more sense if you rented your small farming robot to people in your neighborhood so it could make gardens in their yards. It would be like sharing a lawnmower.
And why stop there: I could sell its services to the city for it to do multiple things when I don't need personal service from a robot.
The key insight you should incorporate into your thinking is that not all robots will be equal. Depending on the type of task and the scale of the task, it will make sense to use different kinds of robots. Renting small, privately-owned robots from random citizens to do big tasks will be inefficient for most large enterprises.
For example, say there's a large university campus with several large, grass fields. It wouldn't be efficient for them to hire 50 local people to come there each week and mow different parts of the fields with their push mowers. The best choice is to hire one professional landscaping company that uses extra-wide, zero-turn mowers and can get it all done in one day.
But if I'm not willing to sell its services, the city could have its own helot droids that run a collective farm all the same so that there's never a food shortage. After all, I live in an apartment, so my prospects for a backyard garden aren't great... but I could always rely upon these helots for backup.
The best arrangement for you would be to rent space in a community garden or vertical farm community garden, and to send your robot there to tend the crops and bring them to you when ready.