The mentality you're describing is certainly abhorrent and disgusting (arguably as much as the content of these videos), but there's a simple explanation for why this disconnect of outrage over animal abuse occurs, while simultaneously couldn't caring less over human suffering.
Humans are seen as moral actors with agency, and so they're generally seen as the source of good and evil in the world (discounting philosophical and theological arguments), whereas animals are seen as incapable of acting in morally good or evil ways (it's true, animals aren't capable of moral reasoning, but some do feel more complex emotions like empathy). When you see humans acting in morally evil ways against animals, it's like punishing a five year-old for a 25 year-old's crime. The five year-old literally can't comprehend right and wrong, let alone being quite incapable of behaving in morally bad ways (especially the way a 25 year-old can). But evil actions against humans are usually perceived as being deserved. People are more likely to ask what he did. People don't ask that of animals and children. This is why the default reaction of animal and child abuse is horror and the default reaction (generally) for abuse towards (adult) humans is apathy, followed possibly by curiosity.
If you run an experiment where you show some horrific video (like a cartel execution video) or something like this (mob lynching and street justice), but you prime the viewer with information, you will typically get the expected result. If you were to prime them with information like, "this person raped and murdered a child," then you may possibly even measure dopamine in the viewer. If you were to prime them with information like, "this is an innocent person and a loving father of three children," you would get full horror and anger from most viewers with zero feelings of schadenfreude.
