It's also a side effect of capitalism, which sells the myth of "pragmatism" and "getting down to business", as well as the "There is No Alternative" way of thinking ushered in by Thatcher and Reagan, that still rules most of politics and economics now. Basically anything about hope for something different, some other way of living the future, etc...is dismissed as "dreaming", "not having your feet on the ground", not "real people issues", and all that right-wing (but now mainstream) way of thinking.
So that means that the very concept of imagining something else, having hope for a different tomorrow, etc...is seen as a laughable utopia, or as being "disconnected from reality". That's exactly what all right-wing politicians say, and a lot of people agree, even some of those who do not vote for these politicians. Obviously all of this trickles down to all spheres of society, including art. It even transformed art into a business like any other (especially in countries where art might not be that subsidized), used more to get paid than to actually express oneself. So if you want to get paid, you do what sells. And what sells is not positive and forward-thinking stuff, seen as "unrealistic". All the reboots, sequels, spin-offs, prequels etc Hollywood is making is also an indication of that in a sense, imagination is quite low in general these days, because it's damn-near frowned upon in politics and economy.
That being said, there's a lot of painting, photography and whatnot that portray Black people in a positive way, and gives images of possible futures and whatnot. Litterature too. I'm more aware of this coming from Africa than in the US, but it must be out there too. Afro-futurism and a new wave of knowledge of self has helped in that matter. Must be there in the US too but maybe not that much in the mainstream yet.