>>281571324
It was the plan of his bosses to turn Denji into a weapon. I think he's just following that plan, because that's all he's good for. Everything him and his organization have done is based on the bullshit that Death Devil herself has fed them.
That's why they were so shocked when she suddenly stopped co-operating with them.
Otherwise you never see Fumiko and Yoshida lose their composure like that. They realize at that point that they've been swindled all the way.