In a sense, that's true. But we're also talking about making arrangements while we're alive, knowing that our wishes now will translate into action later.

If I plant a tree so that my grandchildren might enjoy the shade, I'm still making a decision to do something based on what I believe the effects will be after I die.

So if we're making decisions on where or how to donate our bodies after our deaths, we'd still generally want to choose a worthy cause.