The development of consciousness is a kind of 'mass effect' of the preponderance of broad human types. Through human history; society has been developed by divine destiny to provide a range of experiences to enable these spirits to get the experiences (make the choices) they most need.
It happens primarily on an individual basis: specific individual souls are 'placed' - by God - into specific circumstances: family, class, nation, era etc. But as well as such individual tailoring of circumstances to souls; God has also developed 'the world situation' through history by means of placing types-of-souls at different eras.
Thus, the placement of different types-of-souls at different times through history (as well as different races and nations) itself creates different social conditions - providing different experiences for those who live in them.
So the primary cause is the type of souls placed in mortal life; and a secondary effect is to make different societal conditions in which souls can be placed.
Such linearity of world development continues to provide life-experiences that have never before been seen in human history; and therefore new and qualitatively different possibilities of learning. This is the development (or 'evolution') of consciousness.
This is the merest hunch; but I think that many of the currently incarnated spirits were 'a bad lot' in pre-mortal life; by which I mean with innately a low chance of accepting salvation.
Our present cultural situation - i.e. 'things coming to a point' - the separation of Good from evil, the increased evilness of evil evident from explicit value-inversions - makes the choice between God and the Devil clearer than ever before.
Such moral clarity is, perhaps, the special and new quality of these present times: even more obviously so over the past year.
This current (and still-developing) world-situation probably means that that at least some of these 'hard cases' among contemporary incarnated souls will make the choice of salvation that God so much wishes.
It may not be a high percentage of the people of the modern world who choose to be saved, but it may nonetheless be a higher percentage than would have happened a hundred/ thousand/ ten thousand years ago - at times when good and evil were much more mixed.
Speaking for myself - I am certainly one of those 'hard cases' who was incarnated with a strong innate tendency to refuse salvation. I became an atheist as soon as it was cognitively possible (about age six) and remained an atheist until my late forties.
It was only the increasing corruption of the world that - eventually - drove me to abandon my atheism; as I realized it provided no resources to resist the increasing dishonesty, short-termism and dysfunctionality of my world; and that it encouraged in myself the most horrible and manipulative selfishness and hedonism.
So, recognizing the moral bankruptcy of my atheism; I chose consciously to become first a theist then (soon after) a Christian - and from that decision much followed.
But it was a near thing, and might very easily not have happened; had not 'things' in my world (of science, education and medicine) been getting worse so rapidly.
And had not - therefore - the gulf in motivation between Good and evil been so increasingly obvious.
...I still recall a dream on the eve of my conversion (this would probably be in 2008) in which I saw a globe being covered by darkness; with the darkness being added like black pieces of jigsaw to cover the nations and oceans.
(I knew what was implied by this darkness from my own life and work.)
I saw that Good and evil are sides in a war. And I realized that I had to choose one side or the other: either that Life which was valuable, or incrementally-expanding darkness and spiritual-death.
At last I recognized that the we either take the side of Good - or else we are evil.
And I knew that I personally wanted to take the side of Good.
I suppose that dream was the 'moment' of my conversion to be a Christian; and from then onwards it was (and remains) just a matter of trial and error, and logistics...