Because 5 days is not enough for the market to discover the price of SpaceX.
And the rules were changed so the float is weighted as if it was much much larger than it is.
Additionally with SpaceX they are issuing only a very small percentage of stock compared to a usual IPO, with an unprecedented valuation. Couple that with a much larger than usual amount of the IPO being issued through retail investment platforms rather than to professional institutions (30% rather than a more typical 5%) and it looks pretty unsettling.