It's kind of weird that Gatomon is the only champion that armor digivolves and Salamon, her rookie form, doesn't or can't armor digivolve.
Also Gatomon even needing to armor digivolve in the first place seemed contigent on her losing her tail ring and being reduced to the strength of a rookie. Was the digimental of light placed at its location by the homeostasis/harmonious ones after she lost her tail ring?
Of course the real answer is marketing. They wanted Gatomon to armor digivolve like the others and they needed an excuse for her to need to and they weren't about to have her devolve to Salamon on a permanent basis as a default by still