Name of the phenomenon where characters of a story don't realize something obvious?

I was wondering whether there is a name for the phenomenon or style where characters don't realize something obvious.

This is a style that if often employed in a lot of series, novels, and movies, often (but not always) for a humorous effect. For example South Park does this a lot (people don't recognize sarcasm when people talk about 'sarcastaball', or get a sunstroke when they think they are getting hypthermia), but it is also employed more subtly in a lot of other series (there are, for example, weird names in Harry Potter, but the characters rarely or never seem to notice this).

I think you've at least partially described Dramatic Irony.

Irony that is inherent in speeches or a situation of a drama and is understood by the audience but not grasped by the characters.

The audience is aware of something that a character is oblivious to. This is used for drama as well as humour. If this is not quite specific enough, then already mentioned is the prospect of the idiot plot, which is described as "any plot containing problems that would instantly be resolved if all of the characters were not idiots."

Also, whilst looking at an article on elements of satire, I found the heading Potential Problems with Satire, with this warning -

Misunderstanding: Audience may think the satirist is being serious.

In your question description, you mention South Park and deliberate sarcasm (aka verbal irony, an aspect of satire) being misinterpreted for a humorous effect. Perhaps a makeshift label ought to be 'Extreme Misunderstanding,' or something of the sort, if you truly feel that 'dramatic irony' is too general.

For one last consideration regarding your Harry Potter example, I refer everyone to the adjacent comment, which accurately describes two literary effects dealing with character names.

Dictionary.com

As user191160 pointed out, most of you've described could broadly be categorized as dramatic irony. In a comment you added, you say "In the examples I gave, there is a blatantly obvious, but not necessarily dramatic, fact, that most characters miss." I think you might be misconstruing the sense of the word "drama" here. Dramatic irony doesn't necessarily imply the narrative is intense/emotional/etc. A more basic meaning of drama is simply something intended to be acted out, like a play.

Regarding your example of character names, you may be describing charactonyms/aptronyms. Generally speaking, it's not uncommon for characters to have distinct or conspicuous (or even "weird," as you say) names to the reader. That the characters "never seem to notice this" shouldn't necessarily be taken to have any intended literary purpose. Likewise, a name might not have any intended symbolism behind it at all. For example, a character called "Ruben" might simply be named that because the author liked the name, not to suggest the character is symbolic of a tasty, homophonous sandwich.