Because that version is about the actual topic and not about "so why did you sleep with me".
It would have been nice if you could lead the conversation to the actual topic if you don't focus on the possibly hurt feelings. If you romanced someone else alongside him in Act 1 (or exploited poor Wyll's dance) and he gives you the whole "new true love" speech, the Araj thing also feels slightly redundant to me. It's not heartfelt enough to make the moment of jealousy feel like a step on the way, yet it doesn't add much either.
That's basically where Karlach's special romance treatment in act 1 falls flat for me too. The sex is intended as manipulation and the whole scene is staged in a way that it feels performative while him enjoying the sunshine the morning after feels real - at least that's how it feels to me. He knows beforehand that he can't have sex with Karlach, so why doesn't he come up with a different plan to sink a hook in when Plan A obviously is cannot work? He is usually not that bad at spinning people along or at combining flirtation with manipulation. If you already make all the effort to make a scene specific for one character, you can also really make it work for that one character.
