What causes a 2yr old baby's soft spot on the head not to close yet?

Normal or not ?: Studies in the late 80's documented 2-4% of normal infants retain a detectable soft spot at 24mo. Persistence of this feature is common to medical conditions like hypothyroidism & a variety of named syndromes. If your child is growing & developing well, i see no need to worry over this issue. If there are developmental or other health issues, bring this to the attention of your doctor.