Evolution is not some guiding force that some people are led to believe. It is simply the change of characteristics over time based on trait elimination/reproduction based on how well they allow the animal to survive.
As for washing your back, utility my friend. If your arms could swivel enough to wash your back, they would lose the ability to transfer as much power from your core as you can now. Washing your back is a conscious human need, but not washing your back won't get you killed in nature.
As for people wearing glasses, you've just happened upon something called society or civilization. By living in concrete jungles as we do, moderately safe from being directly exposed to nature, we allow bad traits to pass on because there aren't situations that would cause those traits to be the end of the individual.
Bad eyes, for example: Assuming we lost all technology and civilization as we know it and had to survive like cave men and women, bad eyes, allergies, physical deformities, etc...would quickly disappear. The reason? They are either dead weight and stop being supported by the stronger members with time, or another strong member of nature picks them off.
That is how evolution functions. You're welcome ;)
The idea of evolution isn't about making things easier for you it's about the natural selection of traits that aid in reproduction (including not being killed), therefore these things have not been totally necessary for humans to survive and reproduce and therefore people with those characteristics survive and produce offspring and the genes that code for the traits are passed on.
Compare humans to cats..they are physically so far superior to us in every way!
But don't blame it on God. We have become too addicted to things like cigarettes, and we no longer really have natural selection operating, or people with imperfect eyesight would have been eaten by the physically superior lions!
Our development from conception throughout life are confounded by both nature and nurture. Our genes can make mistakes during mitosis, we can be exposed to less than ideal situations that help shape personality and our imperfections and differences make us unique. Mistakes are part of how we learn to understand the world around us. Would you want to be perfect?
Obviously evolution doesn't create perfect work. How could anyone think random genetic mutations over millions of years would create perfection?
Evolution is about survival. Being able to wash your back isn't necessary for survival.
It's life's little imperfections that make it worth living. If we were all perfect life would be boring.
Religious people would just say it is to test us. You can't argue with religious people. They don't use logic and science to answer their questions. They use their faith, and their belief to answer questions.