Please tell me what causes inside cheek biting habit to form?

Missing teeth: If you are missing teeth your cheeks sag inward so that your other teeth can bite your cheek.Also if your bite is off and teeth are crooked or loose you can also bite your cheek.Poorly fitting dentures can cause cheek biting.

Cheek biting habit: Bite being off, ill fitting dentures, missing teeth can lead to biting your cheek. If you are asking about having a habit, like you catch yourself chewing on the inside of your cheek or pulling off a little of the inner "skin" of the cheek and chewing the piece, which many people do, some causes of that could be boredom, stress, self satisfaction from chewing something which sounds primal.