I have never caught every Pokemon in the game once since I started playing the game as a kid. The reason for this was that I always simply enjoyed playing the game for the story and the challenges that are put before you, all the random trainers, gym leaders, and the villains you have to save the world from create a challenge that allows you to level up and bond with your Pokemon. I enjoyed catching as many Pokemon as I could while the story of the game was going on but there isn't much post-game content to keep me interested enough to keep playing, once the story ends there doesn't feel like there is any significant challenge to put my Pokemon up against.
Basically what I am saying is that it is pointless to have all of the Pokemon if you will never get a chance to put them up against a significant or fun challenge as all the major obstacles other than the Elite Four are no longer available. Regardless I will do it one day simply for the "Wow, I accomplished the slogan of the series." factor of it. Though I wish it would be easier to catch them all, it is stupid that you have to get certain events and certain versions to get every Pokemon, I wish every Pokemon was already attainable in the game.
