Because it is not sanitary for the same clothes to be worn every day. Skin cells, sweat, dirt, hair and other things make clothes dirty after multiple wearings. It is a waste of time to do laundry every day, so you need multiple pieces of each clothing (several pants, shirts etc.)

While you CAN just get identical pieces of each shirt, it is very uncommon. People like to have variety and options so nearly everyone gets different clothes. They also need different clothing for different situations. Few clothing choices work well for ALL of the following situations: the beach in summer, a job interview, a funeral, a wedding, and a snowball fight.

Wearing the same green shirt every day makes people wonder “How long has he been wearing that shirt? It must smell. Does he ever wash it? How many dead skin cells are on there?” It makes people go down a rabbit hole of “ick.”

However, if you choose to do that, it’s your right.