That's why you see Ho-oh in the first saison, he resurrect Ash and Pikachu, that why he didn't grow up and why Pikachu is so OP (like the three legendary dogs maybe ?).

Have you seen the last trailer of the 20th movie ?

Yes, Ho-oh is there, and he is not more "hidden" in the sky.

I bet all I have that there is something behind this.