For the same reason, the Soyuz is by far the most reliable way to pretty much anything into space. The technology is old and trusted and more or less "just works".
The Shuttle was practically a much more useful research spacecraft, crammed with useful things like living quarters, but all the creature comforts and usability mean reliability takes a nose dive and costs sky rocket, pun intended.
Sadly government administration is to blame for the failure of the Buran, Russia's Space Shuttle clone. In many ways it was superior to the American Shuttle, but ultimately bad management and funding cuts meant the project was shelved and they weren't even able to house the retired ship properly.
"Buran could stay in orbit for 30 days, while the American shuttle had a 15-day time limit. It could deliver into orbit 30 tonnes of cargo, compared to the US shuttle's 24 tonnes of cargo. It could carry a crew of 10 cosmonauts, while the American shuttle could carry seven astronauts. Preparation for the Energia/Buran launch at Baikonur Cosmodrome only took 15 days. However, it took one month of preparations before the US shuttle was launched from Cape Canaveral.
The Energia rocket booster could be used to launch various payloads into orbit, whereas the American shuttle's booster was one-task. A year and a half before the Buran launch, Energia was launched with a full-scale mock-up of the Skif-DM orbital combat laser platform weighing 77 tonnes, measuring 37 meters long, and over four meters in diameter. Though the mock-up failed to reach the desired orbit and fell into the Pacific, the Energia booster did its job fine, delivering the huge space platform into intermediate orbit, 110 kilometers above the earth's surface. But the most important difference from the American model was that the Soviet spaceship could perform the flight and landing in totally automatic mode, which it brilliantly demonstrated on November 15, 1988.
Buran's American counterpart used to land with switched-off engines, meaning it could make only one landing attempt. The Soviet spacecraft could take several tries if needed. When Buran approached Baikonur Cosmodrome and started landing in 1988, its sensors registered too strong side winds and the robotic system sent the huge machine for another rectangular traffic pattern approach, successfully landing the spacecraft on a second try. The Buran shuttle was designed to perform 100 flights to space, while its engines were ready to do 66 flights without replacement. During its flight, it lost just eight of its unique thermal-insulation tiles out of 38,800."
Another interesting thing I read about Buran is that apparently (some of?) its computers were ternary, not binary. Unfortunately, I cannot find any English mentions of that, and a quick search in Russian did not produce anything reputable, so take it FWIW.
The Shuttle was practically a much more useful research spacecraft, crammed with useful things like living quarters, but all the creature comforts and usability mean reliability takes a nose dive and costs sky rocket, pun intended.
Sadly government administration is to blame for the failure of the Buran, Russia's Space Shuttle clone. In many ways it was superior to the American Shuttle, but ultimately bad management and funding cuts meant the project was shelved and they weren't even able to house the retired ship properly.
"Buran could stay in orbit for 30 days, while the American shuttle had a 15-day time limit. It could deliver into orbit 30 tonnes of cargo, compared to the US shuttle's 24 tonnes of cargo. It could carry a crew of 10 cosmonauts, while the American shuttle could carry seven astronauts. Preparation for the Energia/Buran launch at Baikonur Cosmodrome only took 15 days. However, it took one month of preparations before the US shuttle was launched from Cape Canaveral.
The Energia rocket booster could be used to launch various payloads into orbit, whereas the American shuttle's booster was one-task. A year and a half before the Buran launch, Energia was launched with a full-scale mock-up of the Skif-DM orbital combat laser platform weighing 77 tonnes, measuring 37 meters long, and over four meters in diameter. Though the mock-up failed to reach the desired orbit and fell into the Pacific, the Energia booster did its job fine, delivering the huge space platform into intermediate orbit, 110 kilometers above the earth's surface. But the most important difference from the American model was that the Soviet spaceship could perform the flight and landing in totally automatic mode, which it brilliantly demonstrated on November 15, 1988.
Buran's American counterpart used to land with switched-off engines, meaning it could make only one landing attempt. The Soviet spacecraft could take several tries if needed. When Buran approached Baikonur Cosmodrome and started landing in 1988, its sensors registered too strong side winds and the robotic system sent the huge machine for another rectangular traffic pattern approach, successfully landing the spacecraft on a second try. The Buran shuttle was designed to perform 100 flights to space, while its engines were ready to do 66 flights without replacement. During its flight, it lost just eight of its unique thermal-insulation tiles out of 38,800."