If I am an indexer, and I need to negotiate a price for Friday closing cross with brokers and proxies (hedge fund and others), I would hope the stock price is stabilized for us to execute such a large size cross.

Assume we know the brokers and proxies have accumulated 70% to 110% of the 120m shares needed, now it is more important to keep a stable environment to transfer the shares already secured safely and peacefully, than to make sure we secure all the 120m shares.

If indexers fall short, they can buy more next week. And when the SP is stable during the a few days before the cross, a seller won't feel they could get more profit if they hold, and they dont know if they have overshoot collectively, and thus it makes the negotiation easier.

If we look at the inclusion month as a whole, the last a few trading day is like a consolidation phase to reach a final price for the Friday cross. The Friday cross includes shares accumulated across many trading days, let us say it is 20 days.

Thus it is kind of reasonable to take a few days to reach a final price for that 20-day worth of effort, instead of finding a balance within the last 10 min of the trading hours on Friday.

So in short, I guess indexers want to take over whatever brokers have got at a stable price, and then buy the rest (0% to 30%) next week.