Because most of the faction leaders are petty and would rather spite the mean Internet man that hurt their feelings than to make an enjoyable gameplay experience for everyone.
Surely that can cover some strategus players, but that's an oversimplification. It's not necessarily "fuck those guys they're assholes they need to get wiped and never have fun again" at all. Some people don't give two shits about the XP, or at least don't consider XP a primary concern. I'm one of them. I don't retire too much, taking every generation to at least 32, if not 33-34. What I am interested in is a "good fight"; I want to engage in a conflict with a relatively well-matched foe, and feel as though every victory against them is well-fought and well-earned. It's almost a MUH IMMERSION thing, but that doesn't cover it either as I am not personally interested in writing RP, although I do greatly enjoy homo-erotic RP posts from our side, especially when they involve tables.
I enjoy playing turn-based and real-time strategy games; ideally Strategus should be similar to that, albeit more dynamic and involved. Of course, it doesn't always (or often) turn out to be that, especially in this strat round, but that's what I'm looking for. So, I must disagree when you say that people don't hold XP battles because they simply want to make someone else's experience worse.
People are also not as likely to hold XP battles because they require some degree of time involved to put together armies, and some people in this round are too lazy to even do that. God forbid they take 45 minutes off of their NA_1 time, or even just take care of strat stuff while they're dead in battle.
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