Like the Soyuz or Apollo spacecrafts, the crew module detaches itself from the service module during re-entry, is it possible to cover the total space-craft with a sleek-aerodynamic heat shield at the time of re-entry thus preventing the addition of space-debris and making the spacecraft reusable up to a certain extent.
It certainly is possible to have enough of the spacecraft shielded to have it all land; that's what the Space Shuttle was designed for. However, if you want to be able to land with a heat shield, you must first get it into space to begin with. The heat shielding for the Apollo Command Module has a density of 32 pounds per cubic foot. In total, the heat shielding alone weighed about 3,000 pounds. Now, if you want to reuse your entire spacecraft, the whole thing would have to be covered in heat shielding, increasing your weight by several thousand pounds, depending on its size. That means that you're going to need more fuel in order to get it up there, greatly increasing the mission's cost. In space exploration, every gram counts and is carefully considered. It's much easier to leave a part of your spacecraft in orbit, to be dealt with later.