New materials were used to manufacture apparel, e.g. thermal technology including materials reacting to the body temperature and perspiration. Instead of absorbing sweat, it is moved on the external side of the clothing to evaporate.
Apparel is now more functional and even fashionable. Jerseys are lightweight but at the same time these protect you from atmospheric agents such as rain, snow and wind.
Technology is applied to apparel too. Different companies are working and sometimes already applied sensors to track your biometric data.
Lastly apparel is more durable and easy to wash, in most of the cases you even do not need to iron these.