Hisself Instead Of Himself.

A poor education?

One probable reason is that it is more regular than the standard forms. The possessive pronoun is used in almost all cases: myself, yourself, herself, ourselves. The exceptions are himself and themselves. So hisself and theirselves are attempts to regularize the pattern.

Mister MicawberA poor education?

That must be a mistake, right?

I don't know why they use it, but Alienvoord might be right. I think I heard "theyself", but maybe I misheard it and it was actually "theirself" pronounced without the R.

In certain dialects of English, for instance African American Vernacular English (AAVE), reflexive pronouns follow a different morphological rule than the standard variety. In Standard American English, we might say "himself" and in AAVE "hisslef" is commonly used, as you point out. Likewise, SAE prefers "themselves" while AAVE prefers "theirselves." Dialects that use these nonstandard reflexive pronouns are, in fact, more in line with grammatical rules than the standard.

Consider how reflexive pronouns are formed in English. The word "you" becomes "yourself," just as "we" becomes "ourselves" and "I" becomes myself. The SAE formation in the examples above, then, are actually irregular since they don't follow this rule. AAVE (and other dialects) follow the regular rule, and from that point of view their construction is more grammatical. Can a structure that uses the regular rule be considered in violation of that rule?

As to your question of why some people use reflexive pronouns like "hisself"--people speak the dialect of those around them. There is no inherently superior dialect. SAE is simply the dialect of the power-holders.

Maybe like with the Irish the "own" is understood -

His (own) self

It's possibly an innate intelligence with regards to correct grammatical usage which you misinterpret as a poor education
Possibly you mistake correct usage in defiance of omnipresent popular incorrect usage as a lack of education.
After all, you wouldn't say "he went out to him car and sat in him driver seat and drove to him place of employment, so why on Earth -or any other planet, for that matter - would one refer to one's self as "him self"?

Using the word "theirself" would imply collective ownership of one self shared among many people, such as the "Borg" in Star Trek episodes.
"Their selves", or "their-selves" would be technically correct.
Saying "his self", or "his-self" would be technically correct, but only a few of us really neurotic people actually care about technical correctness any more (wink, haha, etc.)
The British, whom so many credit with "proper" speech, gave up on correctness long ago, omitting entire syllables from the pronunciation of words, the cause being that they couldn't be bothered with pronouncing them.
They probably invented elision.
The sauce that was apparently invented in their shire of Worcester illustrates that fact quite well for any one around the world using the afore-mentioned sauce.

brianb65101Saying "his self", or "his-self" would be technically correct, but only a few of us really neurotic people actually care about technical correctness any more (wink, haha, etc.)

Those words are not technically correct. You might think them more logical, but they are, in most varieties of standard English, incorrect.