Because it makes it possible for Star Trek writers to create drama and make cogent observations based in real human experience and emotion, instead of generating reassuring pablum that serves no better purpose than making viewers feel smart for watching and nodding along.
This business of "commenting by creating some other world where it's happening" and representing important problems through symbolism and analogy has become trite because our culture has moved on to deal more frankly with human nature in our popular entertainment - if the creators so choose. Two generations of Trek producers have used it as an excuse not to really engage problems directly. It's led to a lot of weak tea and storytelling misfires, things like "The Outcast" on TNG or the episode in Enterprise where they pretended to be standing up for human rights by having the Vulcans forbid mind-melding.
When TOS went to a place like the warring planets in "A Taste of Armageddon," Kirk at least had to come to grips with our own tendency to violence. "We're killers...with the blood of a thousand years of savagery on our hands..." or words to that effect when the Chancellor of Eminiar threw our shortcomings and failures back in his face.
Picard got to wag his finger at less-evolved civilizations because Earth, Starfleet and the Federation had become a Utopian fantasy. He got to tell people that if they worked real hard they could pull themselves up to his level.
Well, Starfleet and the Federation are our POV. They're "our people." And what Trek has successfully done is to other our weaknesses and mistakes. It's those benighted people over there who are the problem. Always.
SNW put a stop to that in its first episode, when instead of holding the Federation up as fundamentally better than the locals (which, TBH, he could have if the writers chose, since it is a pretty nifty place), Pike appealed to them by saying in essence, "Look, we fucked up big time and this can happen to you, too."
They reinforced that when Pike cannot defend the perfection of the Federation when put on the spot in the episode "Lift Us Up Where Suffering Cannot Reach."
And again, this week, in "Ad Astra Per Astera."
The 23rd century isn't better because people and institutions are perfect. It's better because it shows us still making an effort and making progress in the future, and our POV characters are idealists with integrity. You know, like many people now.
This is what Star Trek was like, once. Back when it energized and excited so many fans that it endured and its popularity actually grew even when it was in the entertainment industry's rear-view mirror and any revival was a long way from likely, much less an inevitability. And it's a quality that the franchise had largely lost in its Utopian wallow.
Ultimately, SNW is still way more conventional and middle-of-the-road and supportive of the status quo than it could be. But it's a lot better than what we've been getting, so it feels like a big deal.
