Or is it just 'Ukraine fatigue' setting in, which has already for months been observed among the American public, which explains the broader apparent waning interest in the conflict? 

This week Zelensky issued a formal request for FIFA to allow him to share a message of "world peace" just before the kickoff to the World Cup final, scheduled for Sunday, but the world governing soccer body promptly rebuffed the request.

The Ukrainian government is angered and disappointed, given Zelensky has frequently been invited to make appeals before major public events, even including at the Grammys and Cannes Film Festival. This is when he's not already busy addressing the G7 or UN-sponsored events, or European Parliament. It goes without saying that the World Cup final will be the single most televised and watched event across the globe this year.

According to CNN, Kiev's lobbying effort is still underway, but Ukraine officials were "surprised" when FIFA quickly reacted negatively: 

The source said Zelensky's office is offering to appear in a video link to fans in the stadium in Qatar, ahead of the game and was surprised by the negative response. It's unclear if Zelensky's message would be live, or taped.

"We thought FIFA wanted to use its platform for the greater good," the source said.

Is the Ukrainian leader's 'superstar' status waning?