On airliners, pilot's uniform usually include a shirt with stripes on shoulder. I cannot find examples of pilot without this kind of uniform while in service (either in the airport before departure/after landing or on the flight deck). It seems that during long break they can wear T shirts but use their formal uniform when working.
I fail to see why they should wear such a uniform (wearing a shirt with stripes don't make you a better pilot).
For flight attendants, the uniform reflects the image the company wants to convey. Flight attendant uniforms are thus diverse and different for different airlines. But a pilot's uniform is more uniform from one airline to another.
Do airline uniforms for pilots, which do not use shirts with stripes on the shoulder, exist?