He was fired because he couldn't stop talking to the press/leaking unintentionally. He loves the attention, so having a podcast is the perfect thing for him. He has Trump's best interest in mind, but he couldn't help himself from going to the media.

The White House and overall governmemt structure he was expected to fall in line with as part of the administration was suffocating his real potential and ability. He is better off and of more use to Trump outside those confines.

I dont know enough about Bannon I probably shouldn't comment but I feel sometimes trump may not have had many options or it was strategic i mean everyone he tried to get rid of or bring on his team they would mercilessly go after him for and the person and find reasons to ruin those people reputation family and sow distrust with the public