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human
[The Witcher series] Why are the Witchers on decline as a population and profession? how many are left?

i mean, yeah they can't reproduce sexually but it doesn't seem like finding abandoned kids is that hard. you find a house full of em in 3. even if 2 in 10 make it it should've taken a lot longer to decline from a full school occupying Kaer Morhen to the 4 dudes we see in 3. also as a follow up are any other schools still functioning like the wolf is by the time of 3? please avoid spoilers if possible for The Witcher 3 game as i just started it, i just finished Kiera Metz's quests and I'm only level 6. if not, go for it.
gpt
Each school had a personal ruin and an overarching reason. The overarching reason is the decline in Monsters since the Conjunction of the Spheres. Yes, monsters breed. Witchers are also very good at their jobs. 

So you see less monsters, people hold Witchers in less respect because they're not as valuable. They turn from heroes, to tradesmen, to hucksters. Sure, everyone's seen a wraith, or a drowner - but with proper precautions they'll leave you be. Something burns your village? Get the army! It was probably oru neighbours! And as Witchers fade from the world, old tales get retold, and certain memes gain prominence.

We don't know the exact reason each school fell to ruin, but we can take a guess at most. Mages certainly played into at least one, probably more. Their disinclination to help would tamp down on recruits, too. The trial of grasses does not DEFINITELY require a Mage (Leo, for example, was intended by Vesemir to take it) but it becomes exponentially more fatal without one. So let's hit each school. I've ordered them from definite knowledge of their downfall to supposition.

Wolf: The Monstrum incited hatred and lynch mobs, as likely intended by its anonymous author. That author also probably took place in the attack that destroyed Kaer Morhen, since a mob of peasants could not have taken the castle. This might be due to mages not liking the supernatural competition - even if most mages are not too threatened by a standard Witcher. Before the death of Vesemir they could potentially have recovered, but he was the glue that held the remaining Wolf Witchers together. 

Cat: The Cat school slowly turned into assassins, thugs and brigands. Eventually an army was sent to root them out - all remaining Witchers had bounties on their heads.

Viper: Vipers come from Nilfgaard. There, Witchers may not enter cities. The place has a powerful, well disciplined army, a group of sun cultists and a deep belief in the state. We don't know what caused them to be scattered, but given the knowledge we have of the Great Sun, its integration with the state, we have three possibilities: 1) They pissed off an emperor, they were painted as non-human mutants for the religious angle and slaughtered by the army and the Loc Grim mages. 2) 'Formally' disbanded, their school falling to ruin and scattering the Viper witchers across the empire. Grandfathered out, if you like. 3) Informally disbanded - pressure put on them by the state, ensuring they had no recruits, and that the school would eventually crumble. This seems most likely to me, given what we learn in 2 and 3.

Bear: No clue. Probably a Skelligen school. Wore heavy armour and used heavy assaults. They used crossbows. Given that on Skellige, monsters are common but interclan warfare is more so (Mostly as minor skirmishes)? I'd assume they were gutted by the locals because reasons.

Griffin: Magickers above most. I'd assume that they were painted as evil sorcerers, a brush normally reserved for mages. So the peasants get the local lynch mob and incinerate them.

Manticore: I've got nothing. We know of them primarily from Touissant, so I'd assume something similar happened to them that happened to the Vipers. Even though Nilfgaard does not interfere, theoretically, with the internal affairs I've got nothing else to go on.