This is not a suggestion, I just wished to inquire before I made a suggestion in the right forum, as to if there was a reason for city creation to have no XP reward. City creation costs credits and locks you down in game for a period of time, far more than lesser activities where you get experience from.
You could make a suggestion. City creation was implemented as an instant activity and cost very few credits, and at that time there weren't as many options for XP as there are now. Considering the credit cost I don't think it'd be exploitable to award XP, although I can't imagine it would realistically amount to more than 5-10 XP per city.