Give the player more freedom to fine-tune their gaming experience by separating the camera FOV setting of ground and air vehicle. Having the same camera FOV is not ideal.
Ground vehicle perform better having a relatively lower camera FOV from air vehicle. On the ground the player might want smaller FOV setting to make object appear larger while in the air the player may want a higher FOV to see more of their surrounding. Separating that vehicle camera FOV setting will allow them that freedom.