Why do Wizards hang out in towers?
10. Symbolism! The tower is an ancient symbol of arrogance and hubris. Look at how high my tower reaches over my demense! Behold my power and glory!
9. Isolationism! Towers represent the idea of someone who wishes to remove themselves from polite society. They are above it.
8. Fortification! There is only one entrance. In order to invade, you must storm up the stairs. There is literally less square surface area to enchant/protect.
7. Visibility! If you wield vast cosmic power, you wouldn't want anyone approaching to be able to hide from you, no?
6. Display of Power! It takes knowledge, engineering and know-how to build a tower, otherwise every peasant would do it.
5. Protection! Robbery, Home Invasion, and Murder were commonplace. Nobody can just break into a tower -- the separation and height protect it from stealthy infiltration.
4. Power! Ley lines and magical sources are more corrupted near the ground. The higher the tower the more energy is available.
2. Freedom! It's cheaper then a castle and there's no lawn or grounds! Upkeep is easy and they can avoid all those distracting mundane tasks that they are forced to engage in.
1. Safety! It provides protection and a convenient excuse for all those irate peasants who are certain that you are the reason all their cows are sick.
And the number one reason for wizards to live in towers --
It's the most efficient layout for storing all their damn books!
Frog God games recently published my opus Alchemy. In it contains a list of magical mortars you can use to enchant castle and tower walls. It's incredibly dense in content. And it's a real book, with a real limited print run. You should check it out and get it on your shelf before they are all gone.