Because it makes a complete mockery of history, because it means they're clearly completely incapable of learning anything in a reasonable timeframe (what were you doing for the last two hundred years? picking your toes???), because it means they cannot possible think like the humans playing them as they work on a totally different timescale, because elf culture would have to either be completely alien or stuck in the bronze age, and finally because it just rubs me the wrong way!