Why does this manga ring well with so many people? I'll tell you.
For a long time. Manga/manhua/whatever has had this problem where they produce these corrupt evil people. They torture our hero, they abuse our hero, they burn and kill men, women, and children. When the hero finally confronts him its always, "Nah, I'll let you go since I'm such a good guy." So many manga have the villain retire or have an "awakening" that such kindness would be shown to him. Of course, a real villain would double down. Prepare a larger army, and take over since they know your secrets now.
The reason so many "revenge" manga is growing is because people are quite frankly. Sick of this holier-than-thou hero shit. "I won't be like the villain". No no you are far worse because you tolerate this stuff and let any capable bad guy with enough power do what he wants but knows they'll be let go because, "You such as a nice guy." A hero who snaps and just can't take it anymore. Going on a rampage because the world wronged him in such a way is now growing as a genre. This entire revenge porn genre is honestly refreshing, but not because its mind-blowing in its plot, writing, or artwork. It's just refreshing because they are doing to the bad guys the things we wanted to see done to them. That is nip them in the bud.
Hell, why do you think Grand Theft Auto, and other videogames where we can cause havoc are so damn popular? The anti-hero or the villain at this point has somehow become the most interesting part of the story, but not because they are well-written but because their "cause" always boils down to, "The world is disorganized"/"I was so-so wronged! I must take revenge!" and then they are stopped. Is this good? Naw, but is it entertaining? Hell yes.
Small note: I blame Goku for this self-jerking mercy shit.
This isn't a revenge story with heavy plot, chess-pieces, hostages, or anything. This is one guy going motherfucking RAMBO.
