Do you know the meaning of the word "reciprocal"? These ANZ teams give free entry for away fans because their own fans get free entry to other away games.
The Panthers aren't in a position to do that because their stadium is too small to let in potentially thousands of Dogs or Souths fans. So Panthers fans are just losing a game and getting no other game in return.
Reciprocal probably isn't the right word (but it was all I could think of) because they aren't all a straight swap like that. The Dragons for example have to pay extra to go to the two away matches at ANZ whilst the Bulldogs get three away away games at ANZ included in their memberships as compensation for the matches in NZ and wherever else they have taken a match too. Panthers could easily include an away match at ANZ against Souths or Bulldogs as compensation, or reduce their prices which they have done.