It doesn’t need to be tailored made. But if you buy a shirt that decently fits, a tailor can fine tune it to your body for a reasonably small amount of money. Getting a shirt tailored can cost 5-15 bucks. It will then fit perfectly.

It’s hard for many people to get properly fitting clothing, as is your own personal experience. A lot of people don’t really care because they don’t have a sense of style or keen eye for fit. That’s fine.

If you want a tailored shirt, take a shirt that decently fits and and can be tailored to you body. Then take that shirt to a tailor.