For the sake of Shantanu‘s happiness, it seems to me that Bhishma didn't even care who will handle Hastinapur in future, and took an oath of staying celibate. So, indirectly I feels to me that they cared for each other rather than the future of the people of the country. Please note, I may be wrong here.
Similarly, he even promised that he'll keep taking care of the throne, whoever sits on it, forever, and it seems to me... without even thinking what the person who sits on it will work like.
These are some facts based on what I saw in serials and what seems to me. I may be wrong here. But I want to know truth. So was Bhishma agyaani and lacked vidya?