Why? Probably (like Myers and Majluf's 1984 pecking order paper), the debt financing comes with better investor protections and if investors are not sure of what they are getting, this protection is more valuable.
SSRN-Modigliani and Miller Meet Chandler: Organizational Complexity and Capital Structure by Alberto Manconi, Massimo Massa:
"We show that organizational complexity is strongly related to stock market-based measures of information asymmetry - i.e., Amihud's (2002) illiquidity, Llorente et al.'s (2002) information asymmetry coefficient, the number of analysts tracking the firm, and the equity bid-ask spread. In line with the predictions of the pecking order theory, firms characterized by a more complex organizational structure resort less to equity and more to debt financing, have higher leverage, display a higher investment-cash flow sensitivity and hold more cash to finance future investment."Cite:
Manconi, Alberto and Massa, Massimo,Modigliani and Miller Meet Chandler: Organizational Complexity and Capital Structure(March, 14 2009). Available at SSRN: http://ssrn.com/abstract=1359762