Because people want them to be ;)
Mechanic that throws you out of comfort = bad for most people. Personally, I like to be disoriented. Back when I played WoW, PvP skirmishes in Stranglethorn Valley had a tendency to involve water clashes in some way. Brutal. You could win some of them just by holding your breath longer by virtue of being an undead, a shaman, or a warlock
Later on Cataclysm, Vashj'ir was the first, and only, water level of WoW and I loved every second. Most people did not
Now, Vashj'ir's case is, I believe, common among water levels: implementing good mechanics for a single level is a waste. What Vashj'ir is right now is not even close to what was planned