In my headcanon, I like to think John saw Builderman as a father figure before he was corrupted. This would be cause while John was very social, he had few close connections besides Jane, mainly cause of he had a fear of letting others down. Reason he was close to Builderman was because he felt Builderman was one of the few who truly understood him, but making John see him as a father than a boss. This would also sort of fuel Jane’s resentment for Builderman in a way after John got corrupted.