1 .Wrong Floor Underneath
Rugs are not meant to cover soft surfaces.
2. Weaving Tension Change
If the weaver changes weaving styles, this can create wrinkling in those areas of structural change.
3. Bad Product
Some rugs wrinkle because they are made poorly. Most of today’s poorly made, cheaper wool rugs come from India and are sold through many of the mass-market rug stores.
4. Shrinking & Swelling Fibers
Sometimes fibers can shrink during cleaning to create wrinkles and sometimes they can swell from the moisture and create curling or buckling. With shrinking, sometimes stretching can help return the rug back to its original shape if the amount of shrinking is not severe. Often inspecting the back of the rug can give you clues. With swelling fibers, you can see curling and buckling that will correct itself when dry again.
5. Bad Rug Cleaning
Wrinkles and lumps from hanging a rug up while too wet may be reversible with pressing if the rug was not structurally damaged from the weight load. Tufted rugs will keep their shape best when dried out flat. Natural fiber rugs are meant to be washed in a rug cleaning facility.
(Information has been quoted from Lisa Wagner, NIRC Certified Rug Specialist)