Because of the problem with ExtraLife's release in Steam.
Steam didn't like that there was a child in the game - Chiaki (Even though there was no sexualization in her direction)
RNG decided to create a vote on whether:
To keep the old Chiaki (ExtraLife would never get into Steam)
or Aged up her (the game may appear in Steam, and also Chiaki will become Lewdable)
People chose to redesign her.