Various statements are made about why you should wear hijab, such as for modesty or for protection, but the real reason that we wear hijab is that Allah SWT has commanded it. Whenever anyone asks you, why do you dress like that, that's the only answer you need to give them.

Allah SWT is the source of everything we have, our existence, our life, our capability, even our goodness. If He ever stopped sustaining us, we would vanish in that instant. If He ever took away what he gives us, we would never have even a speck of it. If we worked for millions of years, we could never repay Him for all that He has given us. And yet He does give it to us, and all He asks in return is that we do our best to obey what He has commanded us. Surely wearing hijab is a very small thing that you can do for Him compared to what He does for you!