1. Those who get motion sick-
As the venue isn’t moving to the motion of the waves at all times
2. More open spaces-
Meaning, there are more places to escape and take time away from the group
3. Selling merchandise-
If merch is a key component to a successful event, a land event definitely wins over sea, because you are not allowed to collect any money onboard a ship. A work-around for this (if you’re really wanting to go to sea) is to sell merch beforehand, and then distribute on the ship, or prior to leaving for the event.