I don't think there is any need for this topic to be closed. It's an interesting discussion.
It is nearly common knowledge that the Matoran came from 'another land', possibly fleeing from a greater evil, maybe it got too crowded and they needed more space.
All we know is that no new matoran have appeared on the island since they arrived there, and that all their ages are staggering.
Mata Nui did not create the Matoran, he came down from paradise (where ever that is) and brought peace and light to the island that they had settled on. Mata Nui gave to the islanders Unity, Duty and Destiny; as they had none of that, and were just seperated across the island, living out their own lives.
How they were created, well....
I don't have the foggiest.