>>57336763In the anime it is explained that they are limited to protected areas like Charizard Valley or Mudkip Farm.
In older games they were limited because they were considered tools that were above average, so when eggs and breeding were introduced the females were limited to avoid their reproduction in early stages of the game.
As the games progress, seeing Starters in the wild or with a gym leader has become common, as it should have been from the beginning (Using the logic that every person who had a pokemon trip received a starter), it is one of many examples that the lore and game mechanics are not always in tune, such as Vikabolt's speed, or the mother Marowak that is an individual case and they mix it with an entire species.
