Yeah, 100% a psychological hurdle on his end, all his wives are ready for him. It's not like he can't afford children or has nobody to take care of his kids even if he can't do so himself. Annoyingly still a pre-pubescent boy in this department when he has duties as king to ensure succession problems don't happen.
I'd actually appreciate it if we see him teaching his kids his Earth knowledge so that even after he's gone, the knowledge, technology and philosophies he brought to the kingdom continues. His will as a "realist" reformer king will carry on. But first he has to have kids... and his refusal to make love to his willing wives is actually quite unrealistic of him, for someone called a "realist".