Why would he go through so much trouble just to recruit an insufferable prick who thinks he's above everybody else? It could be a manipulation tactic, Cuco in Episode 3 has shown to be resourceful and pulls a succesful gambit on Casto. His interest was probably piqued after hearing Casto boast about his family's wealth and his own worth above everybody else. Getting in Casto's good graces could be just an attempt to use him for his money.
While Casto sees the world as a Film Noir detective movie, Cuco sees his world as a mafia movie, which would explain his way of acting as well.Neither Casto nor Cuco act naturally to the setting they're in, Cuco behaves in melodramatic ways similar to Casto's, as if he's trying to emulate a mob boss he's seen in a movie or something of the sort.In a way, this also means that Cuco, while more experienced than Casto, is still rather naïve in the crime business and all of his show is just him and his friends pretending to be gangsters inside of their own little bubble.
