Why are modern people so indifferent to resurrection and eternal life? Because they are all-but indifferent to the question of whether they might live eternally, and in great joy. Such indifference to life beyond death is (in world-historical terms) quite extraordinary, and invites explanation.
But I know exactly the answer - from my own experience as an atheist through my childhood, youth and early adulthood. Men are indifferent to resurrection because eternal resurrected life is understood to be merely an endless continuation of mortal life - and mortal life is experienced as intrinsically purposeless, meaningless and disconnected.
So deep is this experience of 'alienation' - of being a random thing in a material-causal world going nowhere; of 'it all' meaning nothing; of our-selves as merely transient patterns of information... So deep it is, that it constitutes far more than just a 'belief': This is the assumption and basis of our thinking and reasoning (our metaphysical understanding of reality), and therefore alienation is all-but inescapable.
Modern Man thinks meaninglessness, purposelessness and alienation. It is not a conclusion from life experience, but the very texture of his inner experience, as it bounces back-and-forth between his mind and the world of public discourse, each resonating with the other.
Modern Man therefore assumes that eternal resurrected life would be, must be, as arbitrary and futile as our mortal life - only it would be inescapable. Consequently, the usual 'hope' of modern man is for annihilation - nothingness; an end to suffering and the possibility of suffering; destruction of being (or, at least, of the conscious self).
This is probably why modern Man is 'immune' to the core Christian teaching, as described in the Fourth Gospel - where it is made clear that Jesus came to bring Man eternal resurrected life in Heaven.
That is the essence of Christianity - and when this essence has become incomprehensible, or is being understood only in reductionist, this-worldly and reduced terms - then Jesus is misunderstood by false and restricted concepts; concepts un-consciously derived from the assumption of our incoherent and hope-less modern mortal experience.