Adding oceans can lead to more exploration, and more obstacle. Even in physicology humans are more attracted to the ocean "Being around water gives our brains and our senses a rest from overstimulation. The sound around us, from an auditory perspective.
Adding oceans can lead to better transportation method and boats which would benefit guild wars. A lot for people want some sort of transportation you can have multiple people on, and the most common and non-mordern thing are boats.
Vetex said the game being a continent is one of the problems and I agree. Adding boats and fighting pirates on the way to a quest would be very fun, and even though it might stop you from getting to that quest at least you got some entertainment. When you play world of magic on a continent you get bored and just wanna get to point A to point B