Women wear it so they are not judged by their external appearance but rather by their own intellect and character. Also, they wear it to guard their beauty from unfamiliar eyes and to save everything for the one guy who will love, cherish and protect them
You should weave a thread between 1st and 2nd sentence because the 1st can't exist without the 2nd. The 2nd sentence is really about man being the protector of his woman not wanting another man to take his place and woman not wanting her protector to choose another woman to protect. This invariably leads to women being "closed off" so to speak - but, as is seen with muslim women, even they tend to agree with it, (because it works both ways, being veiled theoretically prevents the man from choosing another woman to protect - of course that doesn't hold up in practice).
It boils down to an individual's actions always being geared toward ascertaining the requirements of their perception of their survival. But what happens when the evolution of society yields a very successful society in that the basic needs for survival are available, but not "freely" per se. That's where your 1st sentence comes in as women's intellect and individualism were irrelevant when the hijab rule was created. People are social creatures and rationalize whatever to sustain their core beliefs. The core beliefs are founded on traditionalism so to speak, in that they are the cultural leftovers of the past. Basically, it can be seen as respect at the individual level, depending upon the individual psychology. However, the overall phenomenon is really a case of people justifying their presumption. They use the excuse of "respect for a woman's intellect etc" because it has an affirming affect upon the invididual egos involved.
Your 1st sentence is more abstract as compared to your 2nd. So the survival instinct is stretched throughout an individual's psyche throughout their perception of their circumstance. This leaves us with an abstract base for surviving, rather than the tangible. This leads to a lot of interesting results, but the pertinent one for this is the justification of the "rules of the tribe" in whatever way a particular individual can manage to rationalize it.