Why are we so confident the price will increase after the spot ETF approval if the market doesn't move when a whale like Saylor buys $600M worth?

I'm reminded of what Warren Buffett said about being greedy when others are fearful and fearful when others agreed. Could this be a by the rumor sell the news event?

How are whales buying massive bags without moving the market? Is there another way to purchase Bitcoin without impacting the price and if so won't all these huge asset managers follow the same path so they don't destroy their cost basis?