There are so many Pokemon the writers never put in.
Almost all of Johto Pokemon except Espeon/Wobbuffet/Donphan/Scizor
never get screentime.
Also some Indigo Pokemon such as Exeggcute/Cubone/Mankey and their evolutions are never shown anymore. Also-when was the last time the writers brought in an Arbok or Weezing? This is a crime to those Pokemon.