Some games are boring, but there are enough fun ones.
The question should be why do we enjoy all kinds of entertainment media. It's either because they tick our reward system in a funny way (or neural structures connected to it), and in more general, we humans (at least I, I can't speak for everyone) enjoy and seek new experiences (curiosity) and various forms of entertainment can feel some of those desires, but unfortunately they can become boring (predictable) and are no longer capable of capturing our attention (
http://en.wikipedia.org/wiki/Attention ), especially if the authors are not being original enough.
I can say for certain most things listed in
>>3 are not why I enjoy various forms of entertainment (some including video games), but they may be why some people play MMORPGS (which I find a terrible waste of time, although a handful are better than the others and are tuned enough that someone can still find it 'fun' enough to play (it's still engaging mentally, this can usually only attained by making the game about direct player interaction (simplest would be PvP games, but they shouldn't be about items or grinding, instead should be focused on skill and mental activity - the same reason chess is still popular today))).