What was G-d's plan in having 20 generations before Abraham appears?

Question

I'm trying to understand G-d's plan for creating wicked and sinful humans, waiting for 1600 years/10 generations for them to sin, wiping them out completely, then waiting for another 400 years for the other 10 generations to sin until Abraham (us, the Jews) appears on the scene and starts occupying himself with what the initial purpose of the creation was - studying Torah and keeping its laws.

Our Midrashim keep insisting on the fact that the Jews were the ultimate goal of the Creation:

• "ישראל עלו במחשבה תחילה"
• "בראשית: בשביל ישראל שנקראו ראשית"
• "הסתכל באורייתא וברא עלמא"

and many similar.

So, 2000 years - 1/3rd of the existence of the world was wasted on sinners, WHY?

Answer 1

It's like the story of the wise man of Chelm who is hungry so he buys a bagel, but he's still hungry, so he buys another bagel; but then he's still hungry and they're out of bagels, so he buys a knish and then he's full. Oh silly me, had I just bought a knish to begin with I could have saved some money. Sometimes processes need to add up.

Avraham doesn't appear out of a vacuum, he appears out of a thousand years of Mesopotamian civilization, and is now guiding it to do better. There's the famous Midrash of Avraham being like someone seeing a birah doleket, and deducing that someone must own it. Most translate this as Avraham seeing the natural world as so amazing, it's like a fully-lit-up palace that must have an owner. Others, however, say he's looking at the vast structure of human civilization that preceded him, and realizing it is aflame and in serious trouble -- and that Someone must care. (I believe this last point is from a drasha of a Rabbi Gelernty of the Bronx from the 1940s.)

The Sforno's introduction to Bereishis also points out the recurring theme of "humans mess up, G-d picks them back and gives them another chance." We see that here as well.