my baby is 6 months old. He is rolling from back to tummy only not tummy to back.he doesn't do any other activities like crawling,pivoting.What is the reason

A. Hai good evening !! Babies roll over from back to tummy initially by3 -4 months once they hold neck,head they will be able to turn ,able to sit,tries to crawl around 6-8 months. As baby is 6 months do tummy time regularly it helps in crawling,roll over,holding neck,strengthening abs.