Sales doesn't need to be a reflection of a good game tho. Good marketing, building the hype, very much so helps in that manner. Diablo3 also sold good, because of its predecessor, but in the end, turned out to be not so good, all subjective of course, and then again, Diablo3 only have a small percentage playing it nowadays, compared to the number who bought it.
On-topic;
While I'm married, I do not have any children. And even then, I forced myself to let go of the forced background. Every quest that involves me as the concerning father, primarily the main quest, I just quickly skips through because I'm simply not interested in it. Same goes with all the settler thing. I've build exactly only what is needed in one quest for a faction, which is not the minutemen
Spoiler There is a RailRoad quest which involves building defenses for a safehouse
I am not interested in the settler thing for the same reasons, because I really don't care for providing for those people, I have zero incentive to do so. They did well enough when I wasn't around, they will do well enough with me around doing nothing for them.
Also, it seems very far stretched that I would go looking for my son after 200 years have passed, and without any prior knowledge to the Institute. For all I know, reason dictates that my son is dead, and from that moment, the story should be free. They should let us discover, that there would be a reason to go look.
Do Bethesda know their audience. Hmm, I think so. I also think, they know they could get more sales, catering to a wider demographic. Us "old" ones who have played all the previous titles, are well into our late 20's and beyond (myself am 43) So it makes sense, trying to hook into a younger audience. Is it worth it? Well, from a financial perspective, yes it is. From a game perspective, I feel the price is high regarding integrity to the series as a whole. I think, we just have to accept, that the Fallout universe is entering a new time-period and evolving. For some, it is for the worse, for others, for the better. So *shrug* learn to live with it, or let go.
All of the above, doesn't mean we shouldn't "fight" for a better game experience, or try keep it true to the series, but ultimately, it is not up to us, but Bethesda. I can speak for myself tho, and say, that if there will ever be a Fallout 5, I won't be pre-ordering, and I will likely not buy the DLC's for FO4 if it follows the same lines as the main-game. For that, is to shallow for me, when talking RPG's.