This is called capital structure arbitrage. Some fund managers are only mandated to buy stocks, some only bonds, some only convertible bonds. All are trying to maximize risk adjusted returns for their clients. Because the market is somewhat limited for convertible bonds guys, they end up paying premium for what looks attractive. To correctly price converts is more art than science, they depend on too many parameters, but one of them is expected volatility of the underlying assets. Bitcoin volatility is considered high, Saylor and Mike monetize that.