Because God has a foreordained timetable from before the foundation of the world. Here are some verses for you to consider:
1Pe 1:18
Forasmuch as ye know that ye were not redeemed with corruptible things,
as silver and gold, from your vain conversation
received by tradition from your fathers;
1Pe 1:19
But with the precious blood of Christ, as of a lamb without blemish and without spot:
1Pe 1:20
Who verily was foreordained before the foundation of the world, but was manifest in these last times for you,
Jesus was foreordained to be a lamb without blemish and without spot before the foundation of the world, and he was manifest in these last times for us.
Gal 4:4
But when the fulness of the time was come, God sent forth his Son, made of a woman, made under the law,
The timing of Jesus' birth was according to God's predetermined timetable.
Jhn 7:30
Then they sought to take him: but no man laid hands on him, because his hour was not yet come.
Jhn 8:20
These words spake Jesus in the treasury, as he taught in the temple: and no man laid hands on him; for his hour was not yet come.
Nobody could arrest Jesus to crucify him until the Father's predetermined time had come, and that time was given by way of prophecy to the prophet Daniel who wrote:
Dan 9:26
And after threescore and two weeks shall Messiah be cut off, but not for himself: and the people of the prince that shall come shall destroy the city and the sanctuary; and the end thereof
shall be with a flood, and unto the end of the war desolations are determined.
I didn't quote the entire prophecy, but there was a time, which had been predetermined by God, when Messiah or Christ would be cut off or crucified for the sins of others. This same principle applies to the timing of his resurrection from the dead, the timing of his ascension back to heaven, and ultimately the timing of his second coming, which have all been foretold of according to their respective timelines in scripture.
Even the demons know that God has a predetermined timetable in relation to their judgment:
Mat 8:29
And, behold, they cried out, saying, What have we to do with thee, Jesus, thou Son of God? art thou come hither to torment us before the time?
In light of these truths, the short answer to your question is that everything will play out according to God's predetermined timetable or foreordained timeline, and that is why God has not hit the reset button and started over.