It's kinda like saying "grizzly bears eat the eggs from salmon & leave the meat behind because they're trying to max out calories & get fat for the winter."
Pretty sure grizzly bears don't count calories y'all wtf
They're doing that because all the fat in the eggs TASTES GOOD.
Salmon are falling apart by the time they get that far upriver. Their meat's not very palatable anymore.
So why bother finishing the whole yucky fish when there's more tasty eggs in the river?