[dogscoff]

Depends on your play style. Some ppl like to play the role of a more benevolent superpower who would like to help the little guy out.

Also, there may be strategic advantages: Getting a military alliance or partnership with one of them might extend your range (using their resupply depots) or give you valuable information (enemy ships designs, views of systems you have no presence in).

The thing is, you're right. Playing to win against the AI and stomping them all into the ground really isn't that hard once you've played a few games, so you have to either:
a> start playing multiplayer
b> give the AI a chance (refrain from using certain techs, refrain from trading with the AI, disadvantage yourself at game setup)
c> Play not to win, but for the joy of playing. (usually involves some degree of roleplaying)
d> move onto some other game
e> mod your own game out of SEIV.