It's not towers. It's Tower. All wizard towers are mirrors of the first wizard tower. As all wizards are mirrors of the first wizard. All who become wizards subconsciously connect to the spirit of the first, so they don their robes and pointy hats as the first did, all grow out magnificent beards as the first did, and all build towers as the first did. There is in reality only one wizard and all wizards are he.

Why do we build towers, apprentice? To be closer to the stars. All the magic in the world comes either from the stars or the earth. Earth magic is that of the druids and woodsmen. It makes the plants grow, heals wounds, and governs all beasts. Star magic, our magic, is from the stars it helps break free our shackles to this world. It allows us flight, to conjure objects and creatures into being, and most seductively of all gives us dominion over thunder and fire! Many have lost their way as they chase the stars.. which is why the wise build towers, to bring us closer, so we can listen to their celestial voices. And that, apprentice, is why we build towers."

-Galmanax the Wise of the Alabaster Tower

I like the excuses that rely on practicality.
1) Really tall building means you can see if the villagers are coming with torches to blame you for whatever farming mistake they made.
2) Maybe altitude has an effect on spells. Everything else does. Multiple floors means this isn't a problem.
3) Many separate floors means if an experiment goes wrong on one, it won't ruin the other experiments.
4) Assuming the weird diagrams on the floor do something, it's probably limited to that floor, so again, many small floors = good for keeping experiments separate.
5) If you're lost, you can find your way home real easy. Look for top of tower poking above trees. Or if you're flying, look for thing you might hit.
6) So no one will suspect you have an expansive labyrinth beneath the just-for-show tower.
7) Bedroom on top floor means you can get some freakin sleep. Better if you can't hear the villagers banging on your door asking you to fix whatever they broke.
8) Dragon/Gryphon/Wyvern landing platform.
9) It's important for the elderly to stay physically active, so.... stairs.

Project_Hero wrote:

"9) It's important for the elderly to stay physically active, so.... stairs."
Now all I can imagine is an old wizard on one of those chair things that go up stairs for you.

That's why many wizards learn to fly. All those stairs seem like a great way to stay in shape, until you have to use them every. Single. Day!

BiotopeZ wrote:

5) If you're lost, you can find your way home real easy. Look for top of tower poking above trees. Or if you're flying, look for thing you might hit.

Dark Astoria when it was foggy ...