It can also be observed (and can be worked out logically) that experience leads to wisdom. In other words many experiences deepen understanding of reality.
So as a thought experiment we can draw a vertical line representing the level of experiences and rough corresponding level of consciousness.
As a thought experiment we can take the spectrum of consciousness to it's logical extremes ie total unconsciousness at the "bottom" and total consciousness at the "top". Now any particular being would be somewhere on this line. But wherever he is on the hyperthetical line he is actually experiencing many things and so is slowly increasing in understanding thus rising up the line.
So what ever being we are talking about on the line, they are all experiencing different situations in different sequences etc and thus are slowly rising up the line of consciousness.
This is the case whether or not reincarnation is true or not but it is suggestive of reincarnation if thought about deeply.
If we look at this world of variety then it seems to be a place where consciousness grows. Each individual life is a testament to this. Death seems to stop this progress and yet the bodies that are constantly dying and been recreated are suitable for all different levels of consciousness.
Only reincarnation allows for the continued growing of consciousness in the world. Different body types suit different levels of consciousness. So like a snake shedding it old skin as it grows bigger the consciousness has to periodically change bodies to more complex ones so as to reflect their expanding consciousness.