CatDog's whole thing is that the addition of forward and back aerials, as well as side inputs, probably just makes it so they're taking a bit more time to get presentable. Keep in mind that they were also not among the first reveals for the base game of 1 despite being featured prominently on the box.
So the reason we haven't seen them is likely the same: it's just taking them a little longer to get them presentable compared to the rest of the cast. CatDog was easily like, one of the three or four NASB1 additions that caught the most attention online upon reveal, alongside Hugh, Jenny, and Nigel. They're not going anywhere.