It's worldwide known franchise, and it's supposed to have 8 episodes in 1st season. Even if those will be like 60-80 minutes per episode it will give hella total-time.
If you think that each movie was 3 hours long then here if you will count 60 minutes per episode you will get 2 movies time + 2/3 or third movie...
they also probably want to go global with Amazon Prime to be on level as HBO MAX or Netflix are now and this is best way to do this kind of "launch".
HBO MAX doesn't have any wider reach but this may just push Amazon Prime closer towards Netflix
