“And when the first came, they supposed that they would receive more, and they likewise received every man a denarius.”
When the men who had worked all day saw this their eyes would glisten. Clearly they would be paid much more than a denarius. And they came forward confidently to receive their due. But they too only received a denarius.
The intermediate workers are not mentioned in the final payout, and the assumption is that they too were paid a denarius. But their importance in the parable is in the indication that the estate owner continued to call on people to work in His vineyard all through the day, and called on them to trust Him to deal rightly with them in the end.
We must remember that this is a parable. It is not saying that all who commence work at the very beginning will be dissatisfied at the end, or that none of the others will be dissatisfied. It is using extremes to bring out a lesson. We may in fact happily assume that some would in real life be content with their denarius.