Why Jacob de Rothschild was killed?

Because of the error of Nat and the hospital project on this soil...
That K_pro and the gangs heisted those funds!

That is the facts of the case. They had plotted to steal Woman's sum and they heisted those funds. Because they cannot heist her share from Guy and Philippine de Rothschild.
Lesson learned... you give wjat is the due sum and share of the right ones!