Everybody loves an anti-hero these days. Whether it's the massively successful Deadpool or the growling, scowling Wolverine, heroes that kinda aren't are huge.
Perhaps it's the frustration with the rules and laws that so many people see in their lives.
People get busted due to technicalities while others walk free due to loopholes. Laws that are unfair or unjust may be passed, or fair laws may be reinterpreted in ways that no one anticipated. Whatever it is, there is an undeniable growth in people's anger and fear about the Law of the Land and how it is enforced. Even if you don't agree with that assessment.
We've all had something unfair or unjust happen to us. We each have had that one person who used the rules to hurt us or someone we cared about. We've all had our Umbridge to deal with. We all know what it's like to want to get revenge on someone who was only technically right.
Perhaps it's the freedom that the vigilante style promises. The Merc with the Mouth can say pretty much anything he wants to, and consequences are temporary at best. How awesome would that be? We spend a lot of time thinking about how what we say will affect us, usually through how it makes other people feel. Whether we agree with such consideration or not, it can be stressful.
Perhaps we want to be able to dispense justice where none is available. The Punisher was able to give "untouchable" criminals what they deserved. Of course, that was by his determination. If more people did that kind of thing, they'd likely start hunting each other down. Which might be amusing...
Perhaps we are just sick and tired of having to process so much, care so much, invest so much with so little return. Maybe we would rather not give a damn, like so many anti-heroes do in their own lives. Maybe we want something so sweet and pure that it makes us want to care again, like so many anti-heroes encounter.
The point is, we live in a world with a lot more gray than black and white, perhaps more than ever before, or perhaps that's just the perception we have. Who knows?
Either way, we have a very dark and nihilistic view of the world, right now, as a society. Our heroes and protagonists are reflective of that, and we want our heroes and protagonists to reflect some secret, closely-held part of ourselves.