Because Nuzlocke rules. Can only catch the first Pokémon you see in each area, can't catch another after that. Epifex didn't have the dupes clause, which means you can ignore the main rule if you've already caught the Pokémon.
A kind of self-imposed 'hard mode' of playing Pokemon. Rules vary between people, but the general gist is that there are limits to what you can catch (usually the first encountered in any area), and if any of your 'mons faint, they're dead and gone, never to fight again.
As such, it's actually possible to lose the game entirely. People tend to sometimes make stories/comics and stuff about their Nuzlocke run.
After a few days of reading various nuzlocke comics... I really want to make one of my one... But I'm afraid I might get to attached and take their deaths pretty seriously... Yeah... I have zero balls...
AHAHAHAHAHAHAHA It's 5:45am and I'm about to go to bed (oh holidays, how I love thee), and this. is. the. best. damn. thing. Damn epic enter-epifex-scene, hilarious "fwoosh"...and the pun. Oh god the pun. You're the best, man.
Permission to turn the mudkip-unimpressed-stare into my skype-avatar?