Why was wealth so unevenly distributed in the Hellenistic world?
Wealth was unevenly distributed in the Hellenistic world because that was how things were everywhere during that time and even for a long time afterwards. The reason for this is that the economies were so dependent on labor that individuals generally could not be productive enough to make much money.
In the Hellenistic world, something like 80% of the entire adult populace had to be working on the land. This meant that the great bulk of society was making only enough for themselves and a few other people. When you have a system like that, powerful elites tend to take all of the excess production and leave very little for those who produce it.
Because they had little excess wealth, and because they certainly had no feeling that wealth ought to be spread in a democratic way, the wealth in these societies was very unevenly distributed.