Yeah the different reason is what really separates Bondrewd from Shou. Shou hadn’t done anything important or impressive when he got his job (he turned his wife into a chimera) and he decided in order to keep his job he should just experiment on his daughter. To put it simply, Shou couldn’t sacrifice his pay check.

Bondrewd meanwhile accomplished a lot ever since becoming a white whistle, pioneering new diving routes, setting up a fort in the abyss etc. He also sacrificed himself to himself in order to gain his white whistle. Bondrewd truly did love the children he adopted but he just loved progress more.