Why is the general sentiment that unique, super special snowflake names are bad? Like, it's all fictional, if I wanted some realism I'd just go outside for once.

Well, it's because making up tons of names for things makes shit confusing. Making up a name for something that doesn't exist in the real world makes sense, but calling some sword from a fantasy culture a Dikkinshwab despite it being basically a machete with different degrees of sharpness and ornamentation is just pointless. Sort of like why the legs of a insect, despite being very different in design are still called legs. Or why a alien with a gun based on accelerating clay particles extremely fast may just be called a "particle rifle" instead of a "Zvynpc Iscc".

Well, it's because making up tons of names for things makes shit confusing. Making up a name for something that doesn't exist in the real world makes sense, but calling some sword from a fantasy culture a Dikkinshwab despite it being basically a machete with different degrees of sharpness and ornamentation is just pointless. Sort of like why the legs of a insect, despite being very different in design are still called legs. Or why a alien with a gun based on accelerating clay particles extremely fast may just be called a "particle rifle" instead of a "Zvynpc Iscc".

I have a rule that if a paragraph contains more than three made-up words -- including weird-enough names -- I stop reading. At some point, ENGLISH already.

Why is the general sentiment that unique, super special snowflake names are bad? Like, it's all fictional, if I wanted some realism I'd just go outside for once.

The problem is the effect. Storytelling is basically a form of manipulation - you are trying to get another persons mind to imagine things a certain way and think a certain way. People remember things better if they have some familiarity with them. So even in a fantasy world, you want to use familiar phonemes so that names feel familiar to the reader. That is unless your character is suppose to be foreign in unusual, in which case you shoot for the Polish elves.

The problem with the fancy names in the style of "Silvanius Precrestortude" is that they are pretentious. You can have pretentious characters, but you don't want everybody to be pretentious. And if Silvanius Precrestortude ends up being regular folk, the name comes off as out of place and weird.

Of course, you can break these rules for effect, but you kind of want to know how to follow these sorts of rules so you know how to break them properly.