>>55291792Two reasons, mostly.
Some pokemon (aka: 'mons like Gible) are completely out of the way, people just miss them entirely. I could go as far as to say that Lucario is also pretty out there as well, but I digress.
Floatzel usually ended up on peoples teams in their place, and the box legendary typically ended up on kid's teams.
The second reason is because the variety in the early-game is pretty much tailored to giving you 5 'mons that could theoretically take you through the whole game, save the 6th slot which can be whoeverthefuck, such as the box legendary or Lucario.
