Yes, good reasons. But you forgot one!!! They get kicked out of games because other people assume that they don't know how to play. Happens to me every time. Seriously! I haven't been able to get into a game at all.
I almost forgot, one more thing. Alliances. Diplomacy works. There is nothing better than having an AI ally show up and help you smash an enemy fleet. On the other hand, it is exciting to see an enemy fleet have it's ally show up in your system to help them try and defeat you. If you can take on the combined fleet (alone or with your ally showing up, too), then you have experienced a great battle.
IF you play 2 to 4 hours before having big battles, you should expect the computer to retreat. Why? It is simple. Your game galaxy has been developed. The computer will attack but you probably have well defended systems. So, why would the computer want to let his whole fleet be destroyed in an offensive strike? Second, if you attack his forward positions, the AI again probably would rather lose them and keep some of his flee
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Honestly, I doubt that our civilization will make it that far. In the extremely unlikely scenario that we do, our planet will have a dominant government and so, at least for the early stages, will be united in the exploration and colonization of other planets or asteroids.