I find it odd myself to like a post about someone's death, but I try to remember that some people use the like button to mean something more than "like." I don't know why, since the button says "like." But it has turned into a multiple meaning thing.
When FIL died I posted about it on FB. I got a few likes. I decided to believe these people were "liking" my sentimental comments about FIL rather than the information about his death.