Well that svcks...
I don't even care if they include a lot of underwater combat, I just want the content to explore. Then again I am a surfer and diver irl and very few games even do underwater content at all. Which is a shame.
Why? Just because other devs svcked at implementing it? Why is it bad? Why don't you enjoy it? If you don't mind me asking.
Partially implementation -
for WoW is was the movement slowdown (which made it excessively tedious) and the weird way they implemented the breath meter.
for GW2, the 'everyone has rebreathers' made it rather pointless.
Also in both cases, combat felt more than a little off, as games generally don't deal well with three dimensional interaction.
Partly it is the unreasonableness of a lot of underwater adventures. I prefer more traditional fantasy, and spending a lot of time underwater just isn't something people can do, or are willing to do. At some point the suspension of disbelief breaks.
As for content, they have an entire continent to do- and they're including maybe a third of it to start with, so they have a lot of places to fill in before they get to the sillier stuff. It is also a matter of the resources necessary to make underwater combat (or even movement/exploration) good. Given that, I'd rather they spent development time on something more enjoyable.