I think I have some idea, why Polynesia (as AI) doesn't expand - it's a combination of factors:
.) Really unproductive starting location: 3 production from capital + 1 from an atoll nw. No chance of improving production (2 more landtiles are near, but they are jungle - with grassland below) - so the initial production for Honolulu stays really low for reaaaally long.
.) Good growth starting location: IIRC 4 improvable sea-resources lead to comparable quick growth of the capital - soon eating up the happiness-bonus from the 2 or 3 luxuries - assuming you *have* used your valuable production on 1-use workboats (unlike the other civs that can build workers to multi-improve their capitals' ressources, and which are not so strapped for production in the first place)
.) Settling new cities would be quite a drain on the economy - you have to wait at least until late medieval times to research compass before you can form your FIRST trade route - but even if your new cities have some good production going, you *still* have to wait while building a harbor in the really lazy capital as well (or you could buy it... with the money... you don't have... thanks to no trade routes
)
I don't know why the AI wouldn't expand after Compass - then again, it might try to play catch-up in the capital (which, due to limited production, will be sorely lacking in area-appropriate buildings)
Even if geographically incorrect - maybe give them one or two hills (or even some atolls) and see if that helps the AI?
oh, and bad production in Honolulu also means 2 things:
.) Polynesia has virtually no chance to found a religion (no natural wonders for faith, too slow to build faith buildings, scouts used mainly for naval purposes, therefore no goody huts/free faith)
.) No chance to grab any wonder in the first 100 turns. (Playing on Immortal. I had no problem getting 5 or so wonders by this time in my earlier Maya-game - at Immortal as well)
That being said - surprisingly, Polynesia can still hold it's own (score-wise in the top third of civs) - even without wonders, free techs or religion.
Other observations @Turn 110, unless otherwise noted
.) China explores Australia as early as Turn 55 (with land units!). Makes it even stranger, that no one settles there.
.) Selasse leads the scoreboard - all other African nations are in the bottom half.
.) By turn 100, Polynesia has made contact with every other nation (using only its starting unit to scout). Since open borders are only just started being traded and no one else can cross oceans yet - this is hugely different from other nations. (Though not [yet] much of an advantage, as RAs are not yet possible).
.) American, Chinese, Indians Mayans and Russians are the remaining nations in the top 3rd (apart from aforementioned Ethiopia and Polynesia), all with ample space to expand into
.) The Bottom-6 look like they will stay at the bottom: Spain, Germany, Carthage, the Inca, the Arabs and the Byzantines (high-to-low) all have no place left to expand (England could settle Ireland, but that's it)
