We take care, that's how you can take care of your companion
Did ALBERT or BERTA get some stains on your last hike? Or did you drive around the city with the bike without fenders? Just take a sponge, rinse it with luke warm water and wash the stains out. If you use soap make sure it is colorless soap on bright fabrics. Feel free to use gall soap for stubborn stains as the colors of the fabrics don't wash out. The straps are 100% Cotton you can rinse them with hot water as well.
Backpacks are items of use where wear is normal. The nicer you are to them, the nicer they are to you.