Satin is meant to be a smooth material, which means it doesn't stick or grip easily. Satin slides and it can slide while you are sleeping on pillowcases made of satin, which feels less like a luxury and more like a problem when you're in that situation. \
Satin is meant to slide but there are ways to prevent it from doing so on your pillows. Use standard sewing supplies and some basic stuff from a crafts store to add a zipper to one side of the pillowcase, which can provide some grip and some "stop" to the satin material. \
You can also sew buttons onto your pillow and sew little loops of fabric inside the pillowcases to correspond with the buttons. This will keep the cases in place and prevent uncomfortable sliding. \