They ONLY care about settlement building and the institute. At least they do if you only stick with them. It's like BoS doesn't even exist to them. Maybe if you join BoS later, but beforehand? Nope. It's like "Hi. Bye."
Considering that BoS is "freeing the commonwealth" in THEIR way and the in the way of the minutemen (basically genocide of none humans), you'd think there would at least be something to say on the matter between them. Something along the lines of "You act like you're trying to save us, but you're not the holy knights you make yourself out to be."
Btw, how do you trigger the, um... backup of the BoS outside of the main quest? Certain level? Doing other certain quests? After so many in game days/weeks? If it's mission scripted the name of the quest itself will suffice.