I don't know but given that you can't define happiness for someone else, it's a very personal thing, surely it's more insightful to flip the question on its head and figure out how to minimise suffering instead?
Don't ask "what stops you being happy?", instead ask if they're suffering - hopefully most of them are not, but if they are, what can be done about it?
I just have an aversion to someone trying to inflict their version of happiness on others i think.
Often, measures of happiness really means content. It doesn't mean a lack of suffering, but how well you accept it.
Nordic countries for instance are often ranked as the "happiest" even though their winters are terrible, no one is smiling in the streets and they have severe issues with alcoholism resulting in some of the strictest regulations regarding alcohol sales. But because they are accepting of their situation and support each other, they are considered happy.
Don't ask "what stops you being happy?", instead ask if they're suffering - hopefully most of them are not, but if they are, what can be done about it?
I just have an aversion to someone trying to inflict their version of happiness on others i think.