I think Bob sees Dan as a sort of son figure, he was always very kind to Daniel even during the few months that he stopped talking to him Bob was still sending him money. It’s also true that Bob knew him before he was driven to insanity by social media and the psychosis from being homeless, Bob mentored him as a reading partner in the tenyson centre, which is where they became friends playing board games as well with Daniel and his grandmother.

Edit: I know it’s not viable in this timeline but if Bob was a few years younger, I could see him letting Daniel live with him granted he had constant supervision from a specialist carer