This fund does not buy and sell Bitcoin as people buy and sell shares. What Grayscale does is buy bitcoin only to match the private placement of new shares at par value at the time of the sale. Then there is a holding period (it originally was 6 months) for the new investors who created the new shares. My understanding is that right now there is a large number of the new shares that the holding period just ended. Those are on the share that were purchased back with BTC was under $15k. If a large amount of these newly trade-able shares are held by institutions, they will likely lock in some of the gains and "rebalance" with the rest of their holdings.
I think in time, the crypto funds like GBTC will actually buy and sell the underlying assets as needed when people are buying or selling at material difference than the side, they will start acting more like a standard mutual fund.
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