If the question is why wealth inequality has been increasing over time (as opposed to, say, why it exists in the first place, or what the government can/should do about it), there’s an extremely dry answer: it is just the way the math works.

Here's why, for those who are interested:

Let W(i, t) denote the wealth of family i in generation t, and let r(i, t) denote the net return on wealth, after taxes and spending, that family i obtains between generation t and t+1. Then for each i and t:

W(i, t+1) = (1 + r(i, t)) * W(i, t).

Suppose also that r(i, t) is independently and identically distributed across families i and generations t (and that the distribution from which it is drawn has positive variance).

Then it follows mathematically that the variance of log wealth W across families i increases linearly with generation t and therefore does not converge as t goes to infinity. In other words, wealth inequality keeps increasing forever without ever reaching a limit.