Imagine that paper is insanely expensive because it is very labour-intensive to make. People reused paper (https://en.wikipedia.org/wiki/Palimpsest). Cloth is also insanely expensive. People wore clothes long after we'd consider them worn out.

Your job is to wrap mummies, so you use and reuse whatever is available, scraps of completely worn out clothing, or in this case some scraps of paper that happen to have writing on them. Which you cannot read because literacy rates are fairly low, especially amongst the poor working class.