> The inheritors are in a better position to kill the author-- or just allow them to die from neglect-- and are incentivized to do so by postmortem profits.

An estate tax of 100% would eliminate this moral hazard; but the estate tax is already unpopular when its exemption amount means that few estates pay any tax.

> Any benefit from the work being public domain is diffuse, it won't create a windfall for any particular party.

A defendant in a copyright infringement case would have a windfall if the copyright was extinguished as a result of an untimely death.