Why? At one level, probably because, as a diagnosis, psychopathy has pretty solid pragmatic value (the term dates back into the 19th century when it was 'moral insanity') in terms of having some hereditary basis, and predictive value. Most observant people recognize the type when it is described, and can confirm its validity from personal experience.
Also (perhaps) because although all societies in the past seem to have had psychopaths, at a low level of prevalence - psychopaths have almost certainly become more common and much more successful all-round in modern societies.
This because of several factors. One is that psychopaths have considerably more offspring than average. More offspring in modern societies - but not traditional/ tribal societies. There are more niches in modern societies where psychopaths can thrive, and which perhaps encourage mild psychopaths to become more extreme.
The rate of psychopathy was kept low in the past because they would be killed by the societies upon-whom they preyed - killed one way or another (by execution, or ostracism and exile - which would usually do the same only more slowly).
Without paternal support (which psychopaths never provide) the offspring of psychopaths would seldom survive. Since the condition is significantly hereditary, such culling of psychopaths and their offspring would keep the prevalence low.
Psychopathy is something that the majority of people can agree is A Bad Thing, at least at the superficial level of public discourse and gossip; because it is selfish rather than altruistic, and seeks immediate gratification rather than long term benefit...
On the other hand; this also gives the idea of being a psychopath some appeal - and there exists a kind of envy of someone who can operate successfully in such a fashion - successfully exploiting other people to satisfy their own wants.
Such characters are quite often an archetypal anti-hero in modern media and society (e.g. a life dedicated to "sex and drugs and rock and roll" - so popular an aspiration for adolescents and young adults - is basically validating a psychopathic life).
Therefore, psychopath is a term that performs an up-front function of coordinating the majority of cooperative (and perhaps pathologically-altruistic) people against a minority of parasites - without solving the problem itself, because modern society encourages psychopathy. Such are the favourite kind of strategies of totalitarian bureaucrats and the mass media: to encourage hand-wringing concern over a problem while actually making it worse.
And then there is the covert agenda, of encouraging psychopath-envy and -emulation by a soft-sell of the psychopath lifestyle as fun and cool - which appeals to the increasingly Sorathic mindset of the Western ruling class.
But psychopathy does not really solve the problem of evil, because it just kicks the can a bit further down the road.
After all, why - from a mainstream secular materialist perspective - is psychopathy regarded as a Bad Thing?
Because it is selfish and short-termist - yes; but then why is selfishness a bad thing (if you can get away with it)?
And why is long-termism better - when nobody really knows what will happen in the future, and in the long term we will all be dead?
If psychopathy is supposed to be bad because it cares nothing for the group - then why is the group supposed to be more important than the individual? And who decides what is best for the group?... Well, we know the answer in practice: the Establishment (governments, media, bureaucrats, corporations) are the ones who decides what matters to the group - as everyone saw in 2020.
The Establishment are very keen on a morality that places the group above the individual, since in practice They get to dictate which group matters most, and what counts as being for that group's benefit of harm.
(e.g. According to Them; the supposed prevention of even just one death attributed to the Birdemic, was worth sacrificing the entirety of the economy, freedom, well--being, and all deaths from other causes to achieve. Disability, disease and deaths from the Peck were deemed not to exist, and not to matter if they did.)
My point is that the concept of the psychopath cannot replace the need for an understanding of evil.
When psychopathy is used for that purpose, then the concept is readily adaptable to advancing the totalitarian/ globalist/ Establishment agenda - which is itself innately evil.
In other words, when psychopathy is used to replace evil; we get more evil.
Which is, I assume, exactly why so many people are talking about psychopaths so much, nowadays.
*A sharp increase increase in usage was broadly coincident with the publication and media splash of "The Psychopath Test" by Jon Ronson in 2011. Since the author seems to be a professional "mouthpiece" for the mainstream ideology, and the book was made a Bestseller, I presume that this terminological seeding and growth was Establishment engineered.