Pikachu, Charizard, and Lucario were all rather synchronistic in their rise to fame.
Pikachu barely beat out Clefairy as the protagonist partner of Red, and that choice led to Ash having Pikachu, and thusly his identifiability, and so his fame. Lucario was not popular when gen 4 released, he was popular only after he was given a starring role in a movie, forced as a choice by Gamefreak who specifically chooses whom to market and has for some time.
Charizard was lucky that Red and Green were the first launch titles in Japan, and not Red and Blue, wherein Blastoise would have exceeded sales as it did in the US (as parents tended to choose Charizard over Venasaur for their male sons), and that would have lead to a powerful Blastoise TCG card instead of Charizard, which then would have made Blastoise the anime selection to showcase evolution.
It's really always down to the anime what is popular with Pokemon.