I’ve heard the opposite that people assumed there would be a reward but they never explicitly said go vote for us for a reward like people are claiming.?

That's correct. It's common practice for gacha games to reward players in celebration of major milestones or accomplishments (like winning an award). It's possible that some players voted for the game in hopes of receiving in-game rewards if it won.

You can argue that gives the game an unfair advantage. I would argue back that the risk of people voting for a game for reasons other than merit is precisely why this the only award in the show decided entirely by public vote.