why DID we evolve into humans?

My view is that your question is implicitly teleological, at least the way it is phrased.You kind of assume, a priori, that there is a 'why', when in fact the existence of humans is just one endpoint of a series of highly contingent events, some guided by selection, others completely stochastic. If we could 're-run the clock' of evolution *even with the exact same starting conditions* humans might look entirely different or not even exist at all.Others have already commented on the various roles of selection, different types of selection, and random 'chance' processes. What must be remembered is that the overall process of evolution is not in any way directed at an outcome. Nor does all evolutionary change necessarily arise from some 'need' on the part of an organism. That easy. A lot of evolutionary change requires trade-offs. Organisms end up with new traits that essentially replace older traits. So sometimes old functionality is lost, never to be regained, when new functionality is acquired. Every organism has evolutionary constraints that arise from its phylogenetic history and limit the possible pathways for future evolutionary change.Hope this helps.
EZ

This may be futile, but let's try and refocus this deteriorated thread. The OP seeks a reason why we are as we are, and sort of assumes we must be a product of some directed process driven by 'need', when nothing could be further from the truth. Nothing 'needs' to evolve into anything in a specific form.
Evolution is a process of 'make do' - the best genetics of what is available in a given generation , surviving a given set of selective influences particular to that specific year, survives and reproduces.
Chance events can have permanent consequences to population structure.
There is no evidence of any 'determinative force' or 'goal-directed process'. The fact we are humans in the form we are is merely a product of chance and a long series of contingent events, both selective and random, that affected the survival of the genes borne by our predecessors.