Thieves get to start guilds, fighters get strongholds and clerics get to establish churches. Wizards get a tower. Seems a little weak if you ask me. But there are some good reasons.
The wizard in his* tower likely goes all the way back to Merlin if not before.
I do say "his" in this case since the archetypical wizard in the tower was always depicted as male. Witches get an even worse deal, relegated to just a hut or cabin.
So for a game steeped in medieval quasi-history and tropes, the fastnesses of the other classes make sense. As does the wizard tower.
The tower represents a sense of isolationism and separation from the rest of humanity. To reach the top takes work, takes effort.
Much like becoming a wizard in the first place.
There are also academic associations. We call institutions of higher learning the "Ivory Tower" not just for their remoteness and inaccessibility to the hoi polloi, but also a reflection of the inhabitants' distance from the affairs of the world.
The Tower (capital T) represents, in the physical, the "otherness" of the wizard.
It can also represent the hubris of the wizard as depicted in the Major Arcana of the Tarot. I always thought the Tower here was allegorical, like the Tower of Babel from the Abrahamic religions. "You can be powerful, but not too powerful."
I am not a map-maker. But in my spare-time (hahahahahaha) I have been picking at a tower that I might feature in one of my games. The top of the tower is for star-gazing and for magic that needs to be done under the sky. The tower also extends down to a lower chamber for darker magics. Maybe I'll make it part of my BECMI campaign I am planning. I do have the ground floor all mapped. There is a statue of a syncretized Ereshkigal-Hecate-Cardea guarding the doorways to the upper levels and lower levels.
Maybe I get my son to 3D print one for me.