time is of essence
There were a number of major bottlenecks in evolution of life on Earth. The first one, it took roughly 2 billion years for prokaryotes to appear. The next one, it took another 2 billion for multicellular organisms (organisms with body plans) to evolve. As a pure game of chance these 2 events are very unlikely to happen. Even on Earth these events happened exactly once during the entire Earth history as far as we know.