They need to make it worthwhile for others to join in. I am sure they thought diadem would create excitement about airships and make it easier, but diadem was a giant missed opportunity and a fail so...

What they should do is spread the exp awards to everyone in the party. They are minimal as it is so it shouldn't be that big of a deal if the exp you got was proportional to your level. If they would do at least that it would be somewhat more enticing then nothing at all.