When summoning your 2nd/3rd pet, it pops up a box asking if you'd like to change the lead pet. I would guess most people who click yes on it do so simply because it's a popup box and they want to summon their other pets, and then have weird pet bugs due to it later (pets disappearing on cc/cash shop being one of the main ones). The actual functionality is... not that useful, and bugged anyways, so I don't really see an argument for keeping it around.
I think pets should be allowed to decide for themselves who they think should be the leading pet. This would encourage a democratic viewpoint within the pet society. Rules: - Each pet will vote for who they think should be the pet lead. - Pets cannot vote for themselves if they were the pet leader last. However, they may still stay the leader if the other two pets vote for him/her. - If you have two pets and they vote for each other, so they each get one vote, then the pet that were pet lead last will lose to give the other pet a fair chance. This is totally not an unhinged idea. Devs, please implement this, thanks.