Too easy to write it off to incompetence. The typical light airplane is not a serious IMC platform except for getting through some stratus.
Many light aircraft have an excellent instrument fit.
The problem is that few private pilots are instrument rated and those who do have an IR often do not fly enough IMC hours to be properly current.
A look at the accident reports shows that the vast majority of weather related deaths are attributable to VFR flights continuing into IMC. Getthereitis is still the big killer and Darwin will continue to weed out the overconfident.