Why do we have to create all the segments when we have to add only the HOE IC segment ?

You cannot insert a new segment in the existing chart of account structure. That is why we created a new chart of account structure with IC segment instead of adding IC segment into existing COA.

That is what companies had to do when they wish to modify their COA. They have to create a new COA with new structure, and a new ledger with the new COA. Then a mapping is defined between the old and the new COA segment values and the data is transferred. Then onwards new ledger could be used and the old ledger could be disabled (remove access) or simply kept active for historical querying purpose only.