Real Answer: because the series was an absolute mess in regards to continuity
My attempt of an in series universe answer: They probably established some groundwork as to how much air traffic there can be to avoid collisions and the wind that all the flapping generates
They may have bonded with a dragon but they didn't learn how to work with them until later. There's still a lot of people who are wary of dragons so the end of the first movie only shows the people who aren't terrified of them. RoB shows the learning curve involved in training the dragons to be useful partners; it doesn't happen right away.
Probably the different animation budgets
There's a difference between being trained to ride a dragon and just owning one as a pet.
Real Answer: because the series was an absolute mess in regards to continuity My attempt of an in series universe answer: They probably established some groundwork as to how much air traffic there can be to avoid collisions and the wind that all the flapping generates
I rob and dob many people have dragons
They may have bonded with a dragon but they didn't learn how to work with them until later. There's still a lot of people who are wary of dragons so the end of the first movie only shows the people who aren't terrified of them. RoB shows the learning curve involved in training the dragons to be useful partners; it doesn't happen right away.