This interests me, because I was one of them.
The question was triggered for the nth time, when reading Colin Wilson; who does this in the space of a couple of paragraphs in Poetry and Mysticism (1970) - one of his Outsider series of books that I am currently reading for the first time (it's hard to find, usually expensive to buy).
Plenty of people have made an accurate diagnosis of the problem of Modern Man - because nearly everybody suffers from it, after all. The diagnosis is followed by a rapid, almost cursory, dismissal of Christianity as The Answer.
Why is it so easy for people to reject Christianity? When by contrast the same people will be prepared to put immense time and effort into (for example) trying to rehabilitate some version of Leftist politics as a possible answer; or paganism, Hinduism or Buddhism as a possible answer?
With Christianity it is a case of glancing briefly in the general direction of whatever preconception of Christianity that one has imbibed, then... Well, I don't like the look of that - straight down the plug-hole with it!
Yet with with anything else other than Christianity it is - let's find-out more, give it some serious work, and see what can be discovered...
There are several reasons. First, that the powers of darkness increasingly rule this world; and so Christianity is subjected to By Far the most pervasive and venomous smear campaign of any ideology or religion.
(Not even excepting 'fascism' - since what people now mean by that term bears near-zero relationship to the Socialist Workers Party of Germany, nor to any other of actual various supposed-fascisms. Fascism is just a Boo word used expediently against any opposition; such that real-life actual fascists such as the black-shirted Antifa, paid for by multinational money, are exempted from criticism.)
Christianity is continually under siege from combination of Global and Western National institutions (governments, politicians, large corporations, law, science, education, the mass media - and most mainstream self-styled Christian churches).
The accusations include extreme opposites (Christian churches are a living tomb inhabited by sentimental old women; yet also highly-organised patriarchal nests of fanatical white nationalist terrorists); but one or another criticisms will strike home for someone who is looking for a convenient excuse to reject Christianity.
Second is sex. Sex is probably the second-most-powerful mass motivator, after religion; absent religion, sex assumes primacy.
There is a strong and correct assumption that Christianity places restrictions on sexual activity; and for many people that is sufficient reason to reject it as evil. (Modern people regard any restriction of their own sexual desires as an evil of the worst - most fascist - type.)
Whatever excuse is used to reject Christianity as an answer - the real reason is very often something to do with sex. Sexual revolutionaries (of all types) have been, for more than two hundred years (starting with Byron, Shelley and their clique), at the forefront of atheism, apostasy, secularisation, Leftism. This continues post 1960s, with each successive sexual/ identity phase picking up the anti-Christian agenda.
Since Christianity is in fact The Answer - or, more exactly, contains the answer; this means that there are many people who, for many generations, have lived and died unsatisfactory lives (and perhaps gone to a post-mortal destination other-than Heaven) because of a hasty, ill-considered, and dishonest rejection of Christianity.
Well, it's their choice...