Coinbase shares tumbled today to their their lowest point since the company began trading publicly on April 14. The market often moves in mysterious ways, but several drivers could be at play, including Coinbase’s high opening price at the time of its direct listing, its reliance on margins that are all but certain to drop owing to growing competition, and the lack of a lock-up period, meaning more insiders might now be offloading some of their highly valued shares, driving down their price in the process. Whether Coinbase’s shares fall…