If I die my family doesn't keep getting my paycheck. The living are expected to work. Financially comfortable "heirs" are not a good that society needs to protect.
The reasons your family wouldn't keep getting your paycheck are practical though (you'd stop doing the work that earns your employer an income). Those reasons don't really exist in the case of "Intellectual Property", and it seems unnecessarily mean to make their loss harsh just because other people's losses are harsh. Although I think it should be more like a few years' buffer rather than a lifetime income.