You can't take genuine pride in what others do without your input. You can take pride in what others do if you had a hand in making it happen, like being proud of a child graduating college or being proud of your actions to promote a political cause but I don't think you can take pride in something in which you played no part. To do so is simply self-indulgent nonsense which eventually take the form of nationalism and exceptionalism. You should be happy when your country or your community or whatever does good things but that ain't pride.
Completely disagree, have you never felt proud of other people?
The issue here I think is that lots of ERA don't see their average fellow Americans as "their own people". They identify as specific kinds of American like being a Democrat, they don't see themselves as having the same identity as a Trumper, for example. In other words, this is why you can feel proud of your siblings or friends but not of a total stranger or someone you don't consider your own kind, it's hard to feel pride because someone you normally disapprove of did something good. America is often led by conservative ideas so it's hard for progressives to feel proud of the things that their country does, because even when it moves forward, there are still all the issues that alienate them.
If the question had been broader, asking people all over the world when they felt proud of their hometown, or their sports team, or the party they support, or their co-workers, things like that, OP would get many more positive answers because the question would aim closer to people's identities even if they personally had nothing to do with whatever made them proud.