I think we all have different experiences with ex coming back. Some of us are lucky or whatever word you would like to use and have all the men at our feet begging for us back and others have exes come back because they want sex or something else which they haven't got elsewhere and it's that sudden lightbulb moment that you were the one to give it to them.
My friend has had all of her exes come back and at first they put on the charm to soon lead to needing money or one guy hadn't contacted her for 5 years and popped up wanting sex because his new wife isn't giving him any.
My friend's ego blows up when she messages me omg guess who just contacted me and then when they end up wanting something, she's like "uh... oh". I will say that from her experience (as none of mine ever came back) leopards don't seem to change their spots and they continue the same behavioural pattern months or years before. Each person is different when it comes to exes and their motives of returning.