My guess is he did it this way to avoid a mangled head or face at his funeral....out of consideration to his family
Seau’s personal problems became very public in October 2010 after he drove his SUV off a cliff hours after an arrest on a domestic violence charge.
http://www.kogo.com/cc-common/mainheadlines3.html?feed=125548&article=10096155#ixzz1tkSBXaWa