Superheroes are meant to inspire hope. Why would you want to convince anyone otherwise by "deconstructing" them?
There's a lot of reasons and some of them are valid.
There's stuff in the vein of Watchmen that I interpret as sort of "remedial capeshit", stories that simultaneously acknowledge the importance of the basic virtues proposed by the genre but also the reality that reality is almost always more complicated and nuanced than the stories we use to build that moral groundwork and often times good people have to do bad things in order to prevent worse things. I think that's easily the least bullshit category. Then there's sort of a step further from realism into relativism with stuff like The Cape and Chronicle and that godawful Brightburn movie that centers on what happens when the same power is bestowed upon the wrong people or people who are wrong, and questions the ethics of impressing your will upon others as a fallible person, which I think is still a valid question to examine but tends to trend toward a rejection of one's own moral compass in favor of deference to authority, which is... at least in my mind antithetical to the virtues of the genre. Which is probably the point, a sort of agnostic rejection of the thesis on the basis of relativism, but it either poses no alternative or a really gay one -- relinquishing your individual power to a so-called authority, which is hilarious because it gives that so-called authority disproportionate power over individuals which is then inevitably misused in scenarios that mirror the very deconstructions that argue for that course of action.
Then there's shit that has nothing to do with superheroes or vigilantism and just uses the conventions of the genre as a metaphor for something several steps removed from the underlying themes, like The Boys, which I think is a reaction to the death of the fantasy of capitalism as meritocracy; a reaction to the realization that the people who succeed in modern society are not paragons of virtue and very often the opposite, that the social system we operate in seldom rewards the virtues that we're told it does and know it should. Which is like, fine, it's not untrue, it's just not a superhero story. Not a good nor bad deconstruction of superheroes because it's not a deconstruction of superheroes, it's a deconstruction of something else entirely.
Then there's relativist-postmodernist wholesale rejection of traditional conceptions of what is virtuous, which is the vast majority of cases and almost invariably a puddle of piss. The most charitable interpretation is that the writers genuinely believe their own bullshit, which is already not a good look, because it means that they believe themselves to be good people despite not fitting into the archetype of what a good person is and so they seek to redefine the archetype so as to redraw the boundaries of the definition to include themselves. Just a whole bunch of mental gymnastics to avoid the pain of admitting that their student loans were a mistake, the same way fat people blog online all day about how they're healthy and beautiful instead of investing that energy into becoming healthy and beautiful. The other likely scenario is that they don't respect the genre to begin with and want to stand out from the crowd by being different for the sake of fluffing up their own resume, which studios eat up if they're trying to "get ahead" of the "bubble" that is stories so universally resonant that they sustained the comic book industry for nearly a century right up until the death of print as a medium and in a broader sense have been rehashed for all of human history. And then if you're a schizo like me you humor the possibility that these instances of relativism and postmodernism and redefinition of virtue in media are not emergent market trend but rather top-down propaganda intended to manufacture consensus and shape behavior, or otherwise divide the working class against itself by cultivating incompatible views of morality. Similarly I'm convinced that the constant emphasis on "found family" is part of the psyop to destroy people's existing attachments and sense of identity with any unifying group or ideology so those needs can be supplanted, but it's also entirely possible that it's an emergent phenomenon due to writers being so fucking annoying and gay that nobody wants to be around them except for other annoying gay retards.
tl;dr there are reasons to do it but those aren't the reasons they're doing it.