Disney realized that Mickey's copyright value is low compared to his trademark value, which they'll never lose so long as the ear shaped icecream never stops flowing.
If your cynicism needs feeding, then know that the reason is that they expanded trademark protection in the courts, and they just don't need to extend copyright anymore. They don't need to pick this fight. Doubly so when they've allienated the party that controls the House due to their spat with DeSantis.