How leaves are produced in Dracaena surculosa 

This picture shows how the leaves develop from the tip of the wiry stem. The leaves of other plants generally come out from the side of the stems. Why ?

Nature will develop many paths for living things to survive depending on the environment  That is why we have at least 8 million species of living things on Earth. 
On other planets far away, there may be other forms of intelligent beings (to me, very likely), not necessary the same form as us because they have different environments. A little difference of oxygen or carbon contents will probably change the forms and lives of the organisms.