This The Mentalist screencap might contain
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The writers and actors don't want those two to get together. In fact, they laugh at the fans that want them to. Which personally I find a bit rude, but I won't get into that. Anyway, their reasoning for them not getting together (at least right now) is "they have más of a brother/sister relationship."
I'm sorry, but every time someone is trying to make an argument for why two people shouldn't be a couple, it's always either "they have no chemistry" o "they have a brother/sister relationship." But I've never seen anyone deny Jane and Lisbon's chemistry, so I won't focus...