Depends on your starting point, but, in broad strokes, the world is getting overall better. Some things are getting worse in some places, especially over short periods of time, and a big part of the goodness is coming from technology, but overall we're getting richer, and less a-holy with each other.
We tend to focus on what sucks now, and forget how much things sucked before :). For example, if you're in the US, the civil rights movement was still happening ~50 years ago. Medgar Evers was murdered in 1963, 60 years ago, and MLK in 1969, 54 years ago.
For an international example, the GDP of China has gone up 100x since 1986. WWII ended just 80 years ago.
There is more wealth disparity but people are still less in poverty than before and have higher living standards. Lower class can still have shelter, food, technology, and new inventions nowadays.
By a modern measure. The 70’s were insanely racist. Better not be gay, let alone trans. A women who wants to be an accomplished professional? Better be ten times smarter than your compatriots, and even then maybe better to marry a man you can work with.
I mean we don't have roving bands of marauders that are raping and pillaging across the land. Most of the world is not starving and there are no ongoing plagues wiping out humanity.
As bad as things seem we are living in one of the most peaceful and plentiful times. We have access to most of the world’s knowledge and entertainment in the palm of our hand.
Not saying things could not be better but they could be a hell of a lot worse.
People who don't see that basically want to live in extreme stress for no apparent reason
Now do the same Maths for just the last decade, and then compare it with, say, the 80s.
Human's judgment of "how things are going" is anchored on what they have lived through, not on how things were long before they were born - nobody is going "Well, we must live in a wonderful World because Ghengis-Khan's Great Horde isn't just surrounding cities and killing everybody inside if they don't immediatelly surrender".
Further, our Economic systems are massivelly biased for First Mover Advantage: bought a house in an big city back in the 80s - congratulations, you're now one of life's winners; you great-grandpappy moved to a plot of land in the 1800s that turned out to have oil - congratulations, you were born one of the greatest winners in life.
So when the trend of improvement reverses you're going to hear people complain, starting by the ones who were born too late to benefit from the "good times" that are now over, which I why you're hearing it from Millenials.
But worry not, if the trend downwards continues, eventually even the average peons with the "merit" of having been born in the 60s will be wiped out since in a downtrend Wealth tries to preserve its position and that's generally done by leveraging political influence to take whatever little bit of wealth the peons have managed to accumulate (which is why you're seeing indebtness go up: that's generally how people's assets end up legally getting taken - they were forced to use it as collateral for loans because cost of life exceeded income)
Also don't get me started on how most of the "prosperity" was achieved with unsustainable practices: it's like overexploiting one's farmland to get a couple of years of bumper crops for sale only to end up starving because the land has become unfertile. Sure, if one only looks at at those bumper years and totally ignores the consequences after those years, it's all wonderful.
Even events that happen with perfectly uniform randomness will cause situations were the event happens multiple times in close proximity.
It's just that we humans just love to see patterns were there are none (and suck at spotting true randomness) and will focus on the purelly coincidental "many of the same within a short time frame" whilst for example ignoring longer than "normal" periods when the event did not happen.
Not saying "doom and gloom posts" have purelly uniform randomness (frankly, I doubt it, as most human stuff tends to have Normal or similar probability distributions), just pointing out that without actually having measured both the events and the non-events, your (and everybody else's) natural perception will be heavilly skewed by the tendency to notice seemingly unusual patterns of events and assigning them meaning when they might have no meaning at all because pure randomness will on occasion by pure complete chance produce such patterns.
In summary: there might be an explanation, but it can also just be pure chance, so beware of expecting such things to have a reason.