Why was the application code completely rewritten for SAP S/4HANA?

Why was the application code completely rewritten for SAP S/4HANA?
A . To take advantage of the simpler data model
B . SAP S/4HANA is now built with Java
C . The optimized ABAP code that we developed for Suite on SAP HANA would not work with SAP S/4HANA
D . To ensure that the code is optimized for SAP HANA

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Answer: A,D