The Qarth chapters are principally an exercise in world-building and mood, a reminder that this is a fantasy series, culminating in a major piece of foreshadowing. It's unsurprising that a TV series that minimizes fantasy and doesn't do foreshadowing would want to change that, especially since the producers are allergic to reduced roles in a given season for actors they like. What is
surprising is that, despite TV Qarth's superficial eventfulness, Dany is just as uselessly passive there as in the books, and in the end there's even less reason for the setting to exist. They might just as well have cut it altogether.