People tend to name things visually if there is some resemblance between the thing and an image, shape, or an idea.
The T-shirt itself also has a surprisingly interesting history. At first, T-shirts had nothing to do with fashion. They were invented in the last decades of the 19th century and used as underclothing by laborers and military men. They were lightweight, easy to wash, and much more comfortable than heavier shirts with stiff collars and buttons.
Back then, going out in just a T-shirt was too informal, something equivalent to parading around in your underwear. However, people started wearing them outside due to their utility and comfort.
Fortunately, Hollywood did its part in changing the situation for good.
Actors in old films started wearing plain white T-shirts in a confident, effortless way that audiences loved. Suddenly, the simple undershirt became stylish. Teenagers especially embraced the look because it felt relaxed and rebellious compared to formal clothing.
