So I stand corrected on this one. It was actually relatively common, it was considered part of custom of the sea. I just listened to episode of the excellent The Constant podcast on this very subject:
The key point about starvation vs dying of thirst thing is that the victims blood can be drunk(as long as you don’t wait for them to die naturally and then for it to coagulate.) It was so common that the British government decided there needed to be a test case to show that it wasn’t in fact a legal defense to excuse killing someone:
Also the podcaster pointed out that while there were plenty of cases of allegedly “drawing lots” (described by the survivors naturally) they all tender to result in the weakest, childless, or for some other reason the one that the crew would want to be the victim, being chosen.