I think what creates overprotective parents are a mixture of contributing factors. 1) Fear; 2) Feeling the need to control; 3) Life experiences; 4) Guilt.
1) Fear is created in parents that have been through bad emotional experiences, possibly through raising other children, or possibly through their own childhood.
2) The need to control others is perpetuated in parents that have lost control in their lives, perhaps in different context or situations other than child rearing.
3) Life experiences dictate to fearful parents who feel out of control when things don't go as planned or unexpected situations arise that they cannot fix.
4) Guilt inhibits a parent's rational response to certain situations that have proven to be toxic to them emotionally.
5) It takes a parent that is willing to accept that change needs to start with them before they will let go of the fear, control, and guilt to which their life experiences have held them hostage and dictate how they raise their children.
After all, everyone is a unique person with their own journey.