To make it confusing to non-native speakers.
Don't be a wise ***.
A wise man has wisdom.
A wise guy has an “intelligent donkey”.
A wise guy is simply a smart a*s but a wise man is referred to as an older very smart person that is worthy of taking advice from because his answers come a lifes worth of wisdom and knowledge.
the people who call out a wise guy are ignorant
the people who call out a wise man are truthful
Yep a wise guy is just a smart*ss