lol I just realized only the last sentence of my post was relevant to the topic, my bad.
That's too complicated man~ *insert "I think therefore I am" argument*
But following my beliefs of that whole cycle of reincarnation, and "we're here because we want to be here"... The explanation of how we came to be in the first place (i.e. what got us into the whole reincarnation mess to begin with, disregarding previous incarnations which would only sum up how we came to be what we are today) is rather vague, but it boils down to us wanting to be here.
There's a reference made in most religious texts regarding us giving in to temptation/desire/whatever as a whole, which resulted in us being here now, trapped in an infinite cycle of desire and temptation (or whatever that damn apple on that damn tree was meant to represent; fruit of something? lol @ my failing @ reading comprehension)
As for why we're
still here, the term "because we want to be" refers to attachments and any debts we must pay as billed from a previous life or lives before this one.
For the record, once you reach the highest point of the cycle you're free from the cycle and back to where you came from, and what the heck you do there is undoubtedly incomprehensible considering if you know, you'd probably be there by now =D