I've thought about this and read/listened to some insightful philosophers and classicists consider this very question. The most convincing rationale I've heard comes from the most eloquent, the most learned, most excellent Nathan Dufour Oglesby (https://www.youtube.com/c/NATHANOLOGY)
He summarizes classical Stoicism in his catchy tune "Be a Stoic": https://www.youtube.com/watch?v=XWuLvsB7UmE
He also spoke recently about classical Stoicism's cosmic paradigm of a living universe: https://www.facebook.com/reel/335961102098589
It's this last point that provides the basis, I think, for Stoicism's sort of renaissance. I say sort of because, as with the Bible, today's constituents often focus on only certain pieces of Stoicism. But it is rooted in this idea that just as various cells all function towards the same purpose of supporting our bodies, so all creatures are part of an interconnected, living universe. This conception leads to the idea that everyone, every station of living being just as with every cell in our body, is in service to a grander scheme. And once more this grander scheme can be used to excuse all sorts of unhelpful acts - so long as they are in pursuit of a greater good.
I myself prefer Epicureanism (there's a catchy tune for that, too https://www.youtube.com/watch?v=8hrit65ZSeM).
Unlike Epicureanism - true atheists - Stoicism had its own theological system, a cosmology bound up in the belief in a cosmic force, a fire they called numa/Dios/physos. Modern Stoicism focuses on 2 of 3 categories within Stoicism - ethics and logic. The third field is Physics, under which is included a theological and teleological system that provides a universal context entirely foreign to the teachings espoused by so many today. Here's a podcast I just stumbled upon that does a good job of detailing the critical role the divine force plays in the universe: https://traditionalstoicism.com/the-religious-nature-of-stoi...
Lastly, the interviews in this podcast with Donald Robertson (Stoic) and John Vervaeke (Neo-Platonist) are really, really illuminating and Vervaeke's in particular addresses your precise question: why is stoicism going viral?
https://www.greecepodcast.com/when-a-philosopher-ruled-the-w...https://www.greecepodcast.com/why-platonism-stoicism-are-goi...
