Matt Levine pointed out to a likely culprit, and it indeed has nothing to do with the business outlooks.[0]
SpaceX sold only 5% of their stock in the IPO. Earliest lockups will start to [partially] expire in mid-August, bringing in further 7% of SpaceX stock to market. If you expect the market to be flooded with >2x volume of supply, you can either sell right now before the price drops even further or hold and wait for the business fundamentals catch up with pricing expectations.