1. Kept alive by the will of God. Essentially because we have something yet to do - repent, accept forgiveness, love, praise, serve...
2. Because we cling to life.
Possible because we have been equipped with free will, so we may defy God and refuse to die when we are called. For a while.
(This is, of course, a profound sin.)
So, part of the increase of human 'lifespan' we observe today in the West is due to reducing the contigent causes of premature death; but part is also due to the refusal to die when called, clinging to a-bit-more-life at any cost and at any price.
And we can, I think, observe that this artificially-extended lifespan is a Faustian bargain - a false hope, a trick, a depraved state.
Death is a terrible thing, due to original sin and the process of synergystic accumulation of sin which was set into play by the original sin.
Thus death was not part of the original plan (or hope) but is a terrible punishment.
Death is un-natural, in an ultimate sense, but must be accepted as just and inevitable in this world, because death is a consequence of what we are.
Yet death is now the way to eternal life - and the only way to eternal life.
We therefore must suffer the terrible and unnatural punishment; but on the other side of death we are promised an infinite gift.
Justice and mercy.
Death may be premature; but there is a proper time for death; which we know when it comes - except we blind ourselves.
Death cannot be defeated, nor can it be eluded; but death can be deferred.
However the price of refusing the call, when it comes, is immediately to fall into an appalling and increasing state of corruption, from which deteriorating state the likelihood of repentance dwindles and dwindles.