It's to show either that you don't care if people are in the shit, or how they get out of it.
It can also be used to show that you don’t understand much about people’s shitty situation.
Both meanings can be used together, to
mean that you don’t understand much about their shitty situation, you don’t care to understand it, and you don’t care how they get out of it either.
Where this came from:
A French writer called Rousseau wrote that a
great princess once said, more or less, that if you have no
bread, there's always cake instead.
When she says "cake", don't think birthday cake. Think pastries and cakes that come in squares that you can slice, which a basically just sweet
bread.
Think of a
posh French princess in a carriage that's going through
peasant land in order to get to the castle. They have to stop for a minute, so the peasants start to approach, carrying
bread baskets. The princess asks what they want. She's told they need
bread, because they don't have any. And this is where she says the line. But you can interpret it in several ways:
1. She's never seen poor people before, and she's ditzy:
"Well, what I would do is just have cake instead, so why don't they just do that?"
2. She's never seen poor people before, and she doesn't care (whilst applying makeup):
"Oh well. Can't they just have cake instead?"
3. She knows they are
poor, and she's being a complete bitch, almost making a joke (staring out the
window):
"Oh well, there's always cake."