A gif animation is like an animated cartoon. Each cell is different. If you want to doa blend in an animation You would need to create the blend, convert it to a shape, ungroup and then place each item on a separate layer (cell).

Personally, If I had a 50 step blend. I would create the blend, copy the layer 50 times, then convert to shape, ungroup and delete the uneeded items on each layer. Then I don't have to worry about object placement.