Even though fans were dying for Season 4, when they finally saw it and realized that many of the episodes would focus only on one character, instead of the whole-family-in-the-pool storytelling of the previous seasons, many people were seriously underwhelmed by what they got.
This, of course, means that scheduling issues have been a huge hurtle for Arrested Development to clear as far as getting everyone together again to film the show.
Having flashbacks with new actors taking on the iconic Bluth family roles would be another way to cure the scheduling problems, without using a solution that had already annoyed fans.
Part of the reason it’s taken so long for Season 5 to get going is that, unlike with many TV shows once they go off the air, the whole cast is still working regularly.