I don't know what Nero will say but I think the reason is simple. The paladins are a different faction in the GO than Nero's. He wants his own special foot soldiers.

He already said the GO can't really deploy the robots in the field without breaking treaties but an internal force to counter another internal force is probably enough of a loop hole.

I'm going to guess perhaps some difficult or lengthy creation process? Or they're prone to unreliability? Or there are threats that work really well against organics, so they would necessitate mechanical agents to deal with them?

Because you don't want to depend solely on the Paladin order.

It's been quite clear that the Global Order is a rat nest of competing factions. Obviously the others will want to negate the edge the Paladins have over them.

I only now really acknowledged the lab table nearby. Shame on you Nero, no food or drink in the labs! And definitely no open containers! AND DEFINITELY no drinking from them!