How can traditional martial arts be useless in a fight?

Lots of people say that pretty much all traditional martial arts(Karate, Kung Fu, Hapikdo, etc.) are useless in an actual fight and that only Muay Thai, Brazilian Jujitsu, and boxing are what works. But how can that be the case considering all these other arts are based off of fighting systems which were used in war? If it worked in wars back then, then why wouldn't it work in fight?