Since your farming land is limited, after the job is done, there is no more work.
For software projects, there is always more work to do. It's an arms race between competitors. Imagine you fire developers to maintain your speed, and your competitor keeps their people to go faster. Good luck to you!
What’s uncertain, however, is whether the work that remains to be done is valuable enough that it makes sense to pay someone an engineer’s salary to do it.
In your analogy, your competitors who keep their people could just as easily end up bankrupt.
sure, but there is not more work that people will pay you to do; that's the important question
What really happens is that your bucket gets filled with more work, and now you are as busy as before. Or did someone else got fired because now you were working twice as fast as them?