Why do folks have problems with these 3 words?

Because they don't care to use proper English, and they're not encouraged to by their parents and/or teachers. They're heading for a rude wake-up call when they get into a real job. There they will find higher expectations.

[Note the three good usage examples.] :o)

(1) People usually hear the word in their heads before they write it down. Since these all sound the same, all three spellings are associated with the sound, but two are less common. Since people are more apt to write down the first word they think of, and "there" is the most commonly used, that is usually the first association that comes to mind. Then the person has to think through the meaning of the context to pick the correct spelling.

However, since "there" is such a common word, it is often overlooked in proofreading, and so the error goes uncorrected.

(2) Once one person uses the wrong word by accident, other people can easily repeat the mistake and do the same.

(3) Because people associate "possessive" nouns with apostrophes, it is common to confuse "whose" with "who's"

and "its" with "it's." Perhaps the same is true of "they're" and "their."

They have such problems because they're unsure, when they're holding their pen, and trying to finish writing. They just want to get out of there.

They're = They are (CONTRACTION)

Their= Thing they posess (HEIR)

There= Place (WHERE)

To answer your question. Lack of diligence in wanting to learn or not understanding the above "Heir, Where, Contraction" analogous meanings.

Looking them up in the dictionary and reading the definitions helps.

Understanding, and memory are learned from repeated behaviors, traumatic, or memorable experiences, Practice, Joy, pain, elation, loss etc... So learn the lesson in a grand way, or keep repeating it 'till you get it right.

I know the difference, I listened in class. Some times we get so used to talking and not writing we forget which is which. My pet peeve is the people who use the word "our" but pronounce it like "are". Ex. we are going to are neighbors to visit.

I don't think it's the concept. If you're referring to typing, some people just type to fast and don't take the time to proof read and realize how "they're" using the word. "Their" brains are moving faster then "their" hands, over "there".

You'll find the same with your and you're.

Lazyness

The Murphys? Their house is over there. They're all daft.......

I honestly do not know why people have such difficulty but I fully agree with you..................

People have difficulty because they all sound the same.

they're- a contraction for they are

their-possessive, meaning that it belongs to them

there- refers to a place

Examples:

They're my best friends.

Their baseball is over the fence.

There is snow on the ground.

because - some people are simply mentally able and some are not. Because the rest world is retarded, would that make your normal intellect genius? standards keep lowering and these are the effects.

If they had a good english teacher in their elementary school this should be know problem.