In the Tv mostrar for Pokemon was good for so many years, but so many of Ash's friends disappear after that region. Brock is the only exception to that because he traveled through Kanto, Johto, Hoenn, and Sinnoh. Ash´s travel pals always disappear they should all come back frequently throughout the mostrar when they seem needed.
Brock should come back in the Tv shows because he seems to know almost everything that's going on in the regions. Everyone needs Brock sometimes if their Pokemon are sick if they are in the woods alone without food. Brock traveled through 4 regions though and he has a job...