They would make blocking a little bit easier. Not make it amazing. It will protect your hand from getting shattered upon a kick too. Also, people don't take Taekwondo and karate seriously because the vast majority of their exposure is to a bunch of kids who go to class 45 minutes a day, two days a week inconsistently and cant fight their way out of a paper bag. They dont realize that Taekwondo encompasses more than just people trying to be elite fighters. If you cant punch a solid object correctly and powerful, you are at a serious disadvantage when you start throwing careless punches as if your hands are protected. No, punching concrete is not the exact same as punching a person barefisted, it is actually more difficult. The proper alignment and fistic conditioning it requires are much higher.
Building a rocket ship is also more difficult than punching someone barehanded but being able to build a rocket doesn't mean you can punch someone in the face barehanded repeatedly without hurting your hand. Breaking bricks might be more difficult but it is also irrelevant.
it is difficult because you must hit them properly with a well conditioned fist. Just like punching people in the face for real.