Because we live in an image-obsessed culture.
Scan the magazines in your local supermarket - they obsess with whether Psh is too fat, too thin, too old, bad skin, bad hair -etc., it goes on and on.
Look at the number of magazines there are of this type, and then conclude - we are obsessed with what people look like, it's human nature, always has been, always will be.
We can be who we are, but we will never stop being interested in how others are - it's not as black and white as 'accepting who you are', the human condition is far more complex than that.
You love your wife, and see past her physical imperfections, she does not, but grits her teeth and puts up with your lifestyle choices.
Why not accept that women are far more body concious than men, and holiday with clothes on - for your wife's peace of mind?