I think your intuition may be based on some questionable assumptions:
- All players will always play rationally, which implies that they need to figure out the best tactics in all situations.
- The players are so risk-adverse that they prioritize avoiding a loss above all else.
To express my point with rhetorical questions, consider:
- Why don’t all games of chess end in draws?
- Why don’t all games of regular diplomacy end in 7-way draws?
As I mentioned earlier, I think, in Diplomatic Go, it is fundamentally harder to achieve a draw, since the victory condition is plurality rather than majority.
In regular diplomacy, it’s quite common for games to end with 3-way or 4-way draws, since the players will often rally to stop the leader from capturing 18 (of the 34) supply centers (SCs), and these draws can be very stable, since the leader might be holding 15-17 SCs, which forces the coalition to unite around stopping them, since the choice is cleanly between forcing a draw vs allowing the leader to win.
On the other hand, in Diplomatic Go, with the victory condition simply being to have the largest score (i.e., not requiring control of a majority of the area on the board), stopping the leader (say by cooperating to kill one of their groups) doesn’t just prevent that leader from winning, but also shifts the lead to someone else, so it doesn’t always prevent losing. The only way to prevent losing (by the weaker players) is to possibly coerce all of the potential leaders into accepting a draw. However, the potential leaders might not want to just settle for a draw, and might rather just want to force the weaker players to decide which leader gets to win. How people might prefer between these options depends entirely on their risk aversion/tolerance and how much they specifically value winning vs drawing vs losing.
To illustrate this concept, consider a slightly modified version of rock-paper-scissors, where the players have the option of offering/accepting a draw before picking their move, and if a draw is not agreed beforehand, they only throw once with the game ending as either a win/loss or draw.
Now imagine that you are playing this game and your opponent has offered a draw before the moves are thrown. Do you accept? If you do, you are taking the draw with 100% probability, which avoids the possibility of losing, but also avoids the possibility of winning. If you don’t accept the draw, you have 1/3 chance each for winning, losing, drawing (assuming that you know nothing about your opponent’s potential biases for picking any particular move). How you would play in such a game (whether or not you accept the draw) depends entirely upon your risk tolerance/aversion.
In game theory (GT), the fundamental basis for understanding such decision-making is that each player will have preferences between different probability distributions over the definite outcomes (aka “lotteries” to use the typical GT phrase). Under mild and reasonable assumptions that these preferences are self-consistent, in theory, a utility (payoff) function does exist, however, in practice, the specific utility function is not obvious and not even feasible to determine without a very precise understanding of each player’s risk tolerance/aversion.
Diplomatic Go (and regular diplomacy) are not only imperfect information games (due to the unknown actions from simultaneous moves and private chat), but also incomplete information games, since every player’s utility function and risk tolerance are not necessarily common knowledge.