Here's why it's wrong:
* "Better" is already a comparative adjective. It implies something is "more good" than something else. Adding "more" before it is redundant.
* English uses a single comparative form for most adjectives. You would say "better," "bigger," "faster," etc., not "more better," "more bigger," "more faster."
Where it might come from:
* Informal speech: While grammatically incorrect, "more better" might be used in informal speech or dialectal varieties of English. It might also be used humorously or ironically.
* Child language: Children learning language might use "more better" as they're still developing their understanding of grammar.
* Other languages: Some languages might use a double comparative, so speakers learning English might carry that structure over.
The correct way to express a higher degree of something good is simply to use "better."