Experience shows that in some cases a human presence on-board would have averted crash.
Signal time-of-flight between probe and ground control (Earth) is in terms of minutes (20 min. for Mars). This makes time-critical operation such as lan ding impossible in real-time. As a result probe are required to be autonomous and this makes them extremely vulnerable in face of expected conditions and possible programming errors.
In the famous Apollo 11 expedition Neil Armstrong had to over-ride on board computers to perform Lunar landing.