Why does the United States military use depleted uranium in tanks?

It’s the extremely high density which helps penetrate the armor of its target.

Lead has a density of 11 g/cc. Uraniuim has a density of 19 g/cc. Almost double.
It is also much harder, similar to titanium, so it penetrates objects that need to be penetrated.

The speed of anti tank rounds made of depleted uranium and fired from a tank, usually, is about one mile per second. Just the round penetrating a tank’s armor, without an explosion, is enough to kill any one in the tank.

Because it makes blowing up the bad guys tanks easier when you use it in the shells and it makes it harder for bad guys to blow up your tanks when you use it in the armour.

Some armor is reactive, which means it explodes outwards to absorb the force of the incoming round.

A tank cannot be too heavy. The side armor is the thickest and anti-tank mines explode through the bottom where the armor is thinnest, and some anti-tank missiles attack the top where the armor is also relatively thin.