The question can also be phrased as: why cannot Men be resurrected by God the Father; because the necessity of The Son seems to imply that The Father could not achieve the resurrection of Man.
The Father resurrected The Son, but (it seems) could not resurrect Men; or, at least, could not resurrect Men to a desirable state - for this, the work of The Son was needed.
(Here we Christians may perceive the abhorrence of some 'pure monotheists' for Christianity; the significant limitation that Christianity places-upon the power of God the Father in saying that Jesus Christ was necessary to the resurrection and salvation of man.)
It may be seen as follows:
The Father was able to resurrect The Son - because the Son was divine, as well as being a Man. This entails that The Father can resurrect the divine, but cannot resurrect the mortal.
(The problem for God the Father was therefore: how to resurrect mortal Men?)
The Son is able to resurrect Man, because he is Man (as well as divine) and has himself been resurrected. Christ has been mortal, he has died as a mortal, and Christ has been resurrected; therefore Christ can resurrect mortals.
Jesus Christ needed to be incarnated and die as a mortal, in order that he could be resurrected by The Father - and this event of Christ's resurrection by The Father (long planned and foreseen) would create the new possibility of Christ being empowered to resurrect Men.
The main objection to the above scheme is probably the limitation placed upon God the Father - but some such limitation is intrinsic to Christianity, due to the Christian insistence on the necessity of Christ.
It is a matter of focus. There is some indication in the New Testament that the resurrection was the focus of early Christian teaching - was indeed the Good News of the Gospels.
I get a sense of there being an analogy implied, indeed stated, between the fact of Christ's death and resurrection, and the new possibility that Men who died can now be resurrected.
Therefore the main explanation for the divine Christ having died at all, was that by his going-through death; and a real death - including the helplessness and despair induced by being sundered from The Father. So that Christ entered death knowing that he could only be saved from death by the action of his Father.
All this is a precise analogy for how Men must enter death, and be saved from death; but we Men are saved from death and resurrected by The Son, not The Father - the Father cannot do this; but Jesus can, and will.