Whilst he lay recovering from his wounds his father, who had little regard for him and wanted to ensure his own position of power set to work.
He had authority when he was hand which his father took.
He had power due to his wild men who had been removed.
He had influence over the Gold Cloaks and guard via Bron etc. This had been removed.
All of his allies and supporters had been bought by his father or sent away whereas his enemies now enjoyed the protection and power of his sister and nephew.
He now has no political authority and no muscle to back his claims.
He was also given no credit for what he did in defending the city. Overall he was not so much disgraced as had his status and power taken by Tywin which left him vulnerable.