Money is like an addictive drug for some people; the more they get, the more they need. And yet like your uncle they are seldom happy. They are like the man of whom the author of Ecclesiastes wrote: "There was no end to his toil, yet his eyes were not content with his wealth. ... This too is meaningless a miserable business!" (Ecclesiastes 4:8).
Why is your uncle this way? I don't know the answer, of course, but I suspect one reason is because he's afraid of failure, and he wants others to look up to him and even be envious of him. To put it another way, I suspect he is driven by pride and by a desire to feel like he's better than anyone else.
He also may think that money will buy him happiness, and the freedom to live any way he wants to. But in reality, he's become a slave a slave to money. Jesus warned, "No one can serve two masters. Either he will hate the one and love the other, or he will be devoted to the one and despise the other. You cannot serve both God and Money" (Matthew 6:24).
Pray for your uncle, that God will show him the futility and danger of what he's doing. Pray also that he will turn to Christ, for only Christ can fill his life with the peace and security he is seeking. And make sure you're building your own life on Christ, for He alone gives us the hope of eternal life.