Just my WAG, but there was supply from those big sells and so the ask price wasn't raised because of the small buy sizes. Price will not rise until that supply is eliminated and there are more demand orders than supply.
The MM's have algo programs to sort that out. Also, we don't know if there were/are staggered/timed limit orders that might be adding slowly in an effort to accumulate without pushing up the price.
Several possibilities. Not one simple answer.
Studying level2 flow would help clarify some of that, but I am too busy scalping etf's to focus on that.
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