Why did they avoid Charlie's name in the film title Willy Wonka & the Chocolate Factory?

What was the reason for the shift from Charlie to Willy Wonka in the film title?

NAACP (The National Association for the Advancement of Colored People, a civil rights organization in the United States to advance justice for African Americans) had the objection on the portrayal of the characters in the book. They didn't approve the book, therefore, they didn't want this film to encourage the sale of that book. They suggested to make Oompa-Loompas white and alter the film title.

Filmmakers decided to call the new bar the Wonka Bar and changing the title to Willy Wonka as a promotional tie-in.

Is it not more of Charlie's journey in the film? Is it for the hint to any supposed deviation from novel to film in the film?

Yes, it is, but they put more emphasis on Willy than Charlie. The author of the original book wasn't happy with the film.

From BBC,

A cast of suitably bratty children, Oscar-nominated songs by Anthony Newley and a disturbing, psychedelic boat ride sequence did not prevent Dahl feeling “disappointed” in the movie.

“He thought it placed too much emphasis on Willy Wonka and not enough on Charlie,” said Liz Attenborough, trustee of the Roald Dahl Museum and Story Centre in Buckinghamshire. “For him the book was about Charlie.”

From Screen Rant,

The NAACP had been critical of Dahl’s portrayal of the characters in the book, and they put pressure on the production to alter their appearance, saying in a statement that: “The objection to the title Charlie and the Chocolate Factory is simply that the NAACP doesn’t approve of the book, and therefore doesn’t want the film to encourage sales of the book. The solution is to make the Oompa-Loompas white and to make the film under a different title.”

From MentalFloss,

10. THERE'S A REASON WHY THE MOVIE STARS WILLY WONKA.

Though the book is called Charlie and the Chocolate Factory, the 1971 movie is named after Willy Wonka. There are two reasons for this: When the NAACP was protesting the Oompa-Loompas, they also demanded that the movie’s title be changed so as not to promote the book among viewers of the movie. The second reason for shifting the main character focus was because the movie was financed by Quaker Oats, who were looking at it as a way of advertising a new line of chocolate bars that they were about to produce. Eventually, they settled on calling the new bar the Wonka Bar, and with that they chose to rename the entire movie after Willy Wonka as a promotional tie-in. (Because really, what better way is there to sell candy bars than with the suggestion of light cannibalism?)

But what was the reason for the shift from Charlie to Willy Wonka in the film title?

From the Dutch wikipedia about that movie:

De titel van het verhaal werd echter aangepast naar Willy Wonka and the Chocolate Factory om beter aan te sluiten bij het snoepgoed dat in de film gepromoot zou worden, en omdat in de Verenigde Staten (die toen betrokken waren bij de Vietnamoorlog) Charlie een spottende bijnaam was voor de Viet Cong.

Translated:

The title of the story was adapted to Willy Wonka and the Chocolate Factory to better connect to the candy promoted during the movie and because in the United States (who were involved in the Vietnam war at the time) Charlie was a derogatory nickname for the Viet Cong.

Screen Rant suggests there are 4 reasons that have floated around over the years:

One is that the specter of racism reared its head again — apparently one of the films producers, stung over the NAACP’s accusations over the Oompa Loompa’s, noted that slaves called their bosses “Mr. Charlie” during the war. Another theory is yet another racial implication: that the word ‘Charlie’ was a derisive term for the Viet Cong by American Soldiers during the Vietnam War.

The other theory is less culturally sensitive and more corporate: since Quaker Oats was using the film to market their Wonka Bar, they wanted a title that best reflected the brand. Whatever the reason, Stuart made the most compelling argument for the name change, saying “If people say, ‘I saw Willy Wonka,’ people would know what they were talking about. If they say, ‘I saw Charlie,’ it doesn’t mean anything.”

All four reasons are also mentioned in this article

Is it not more of Charlie's journey in the film? Is it for the hint to any supposed deviation from novel to film in the film?

Yes, Roald Dahl was disappointed about the movie, and the focus placed on Willy Wonka instead of Charlie's development ₁

But none of the sources I found suggests that the change of title was made as a premeditated hint to any supposed deviation from novel to film.

Another possibility:

I remember as a child that the book was named "Charlie Brown and the Chocolate Factory' when I started reading the book, I was initially disappointed to find that this was not the "Charlie Brown" from the famous comic strip. After I read the book, I was delighted with the story.

Perhaps one reason to change the name was to avoid this confusion?