Here's why:
* "These" is a demonstrative adjective, used to point out specific things that are close to the speaker.
* "Ones" is a pronoun that can be used to replace a previously mentioned noun.
The phrase itself is not incorrect, but it sounds very informal and can be considered slang.
Here's how you could rephrase it for more formal use:
* These (if you are referring to a previously mentioned noun)
* These items
* These things
* These examples
The best way to use "These Ones" depends on the context and your audience. In a casual conversation with friends, it might be perfectly acceptable. However, it's best to avoid it in formal writing or professional settings.