Why is that happening? There are two reasons.
First is the design of Russian tanks. They have a crew of three versus United States tanks which have a crew of four. What is different is that American tanks have a human "loader" who grabs the tank rounds from a rack of them (which are stored behind what are called "blast doors"). The loader physically loads the tank round into the gun, much as you might see an artillery shell being loaded into an artillery piece.
Russian tanks have an automatic loader. The game-changer is that there are no blast doors protecting the stored rounds, so when a missile or another attacking tank is successful in penetrating the hull or turret of the tank, it is kaboom!
The other reason is I'll give credit to the United States supplied Javelin anti-tank weapon/missile. It can attack tanks from the top, which is where the armor on a tank is the lightest. Leading to kaboom and secondary explosions that come from the tank rounds stored in the tank also igniting. Thus, detaching the tank turret from the hull of the tank.