Maybe. But they don't need too many for launch nor does their entry price matter too much. The creation/redemption mechanism handles all the extra buying/selling pressure in real time. Passing gains/losses through to unit holders (not affecting Blackrock).

The major flows happen AFTER the launch, via creation/redemption. New buyers drive price, which drives new unit creation, which buys more BTC via the ETF mechanism. ETF's holdings constantly fluctuate.