Although the aggregate capital share for U.S. firms has increased, the firm-level capital share has decreased on average. The divergence is due to the largest firms. While these mega-firms now produce a larger output share, their labor compensation has not increased proportionately. We develop a model in which firms insure workers against firm-specific shocks. More productive firms allocate more rents to shareholders, while less productive firms endogenously exit. Increasing firm-level risk delays the exit of less productive firms and increases the measure of mega-firms, raising the aggregate capital share and lowering it on average. We present evidence supporting this mechanism.