Why aren't these two resonance structure same?
There are called equivalent resonance structures since the number of pi bonds, lone pairs and sigma bonds are the same. On the other hand, resonance is the delocalization of pi electrons. These structures show how pi electrons are delocalised from ortho position to para position and then back to ortho(on the other side of the molecule). So both the structures you mentioned are different in this context and do have a purpose in explaining the resonance phenomenon.0

Note: This rule only applies to hydrocarbons. In other cases, the two resonance structures need to have the same structural formula to be equivalent.