Because people kept making stupid posts about them, mainly.
edit: But yeah also what the guy below me said.
florges is 1000% outclassed by Sylveon
Donphan is 100% outclassed by Excadrill (even defensively, av exca is possible)
Helioisk and Darmanitan because most everyone agreed on a rank except this one guy who kept bringing it up, again, again, and again.
Florges: Outclassed by Sylveon
Donphan: Outclassed by Excadrill (I still use Donphan though, it's a MONSTER aha)
Heliolisk and Darmanitan: This one is weird, they are both outclassed but some dude kept bringing them up even when discussion had ended.
Every blacklisted Pokemon is there because besides of not being good enough to get a rank, its mention sparks shitty discussions constantly. The conclusion reached list is for Pokemon that have reached their ideal ranking decisively. Mantine got there because it made the thread lose focus, as a lot of people were asking why it was ranked and similar stuff, derailing the thread from more important discussion points. Once the metagame settles down, you can expect to see more Pokemon in this list.
• Mantine is a very Pokemon in which some players don't see any worth. However, it's indisputable that it has a niche, and thus it is permanently D rank. Constantly people asked why it was ranked, so it derailed the thread.
• Florges is 99% outclassed by Clefable and Clefable, so when people try to rank it, discussion gets terrible. Thus it's blacklisted.
• Donphan isn't outclassed by anything, but it's a very mediocre mon with no completely defined niche, and is thus unranked. For some reason people insisted on ranking it, so it was blacklisted to avoid terrible discussion.
• Heliolisk likewise isn't 100% outclassed, but it isn't worth ranking. Someone insisted on it being ranked, so it was blacklisted to prevent him + others from being dumb.
• Darmanitan is 99% outclassed by Charizard-X, Victini, and Entei, and yet the same dude insisted on it being ranked, so it was blacklisted to prevent him + others from being dumb.
Ah. Thanks for the answers everyone. I'll have to keep this in mind for when I too get into discussion.