This is sometimes described as initial caps or start case.
From the blog post "The Initial Caps Trap":
As designers, we have our routines. Some of these are long-time habits that we don’t really think about. One example is using two spaces after a period. The issue for today is the use of initial caps. What I’m referring to is when the first letter of every word in a sentence or phrase is capitalized. Why do we do it? If you’re like me, back in school you learned the rules for capitalizing book titles, names of songs, works of art, titles of papers, etc. Roughly, this involves capitalizing all words except for articles, prepositions and conjunctions. This is called title case and there’s nothing wrong with that. But somehow we let this rule creep into areas to which it doesn’t apply.
However, the term initial caps can specifically apply to something different.
From an article by S Wood at Bright Hub:
With the review of the initial caps examples, choose the one that best meets your needs. What is an initial cap? It is the first, capital letter of a paragraph. This letter is larger in size than the other letters. The three initial caps types are raised, dropped and adjacent. Ornamental fonts for initial caps can give a higher appeal. Why? Such types combine art with a letter. Keep in mind, however, an ornamental cap with a complex design makes it difficult to read the text.
In Wikipedia's entry for letter case, under a section involving sentence case, it mentions the variants initial caps and start case:
Title case (capital case, headline style)
"The Quick Brown Fox Jumps over the Lazy Dog"
A mixed-case style with all words capitalised, except for certain subsets (particularly articles and short prepositions and conjunctions) defined by rules that are not universally standardised. The standardisation is only at the level of house styles and individual style manuals . . . In text processing, title case usually involves the capitalisation of all words irrespective of their part of speech. This simplified variant of title case is also known as start case or initial caps.
So, there is no standard term that is always used when you want to describe capitalizing the first letter of every word, regardless of its function. This specific style doesn't seem be common enough that there has come to be a universal naming convention for it. (To avoid any confusion, the simplest method of describing it is "capitalize the first letter of every word.")
The justification for using this style seems to be that it's simple and avoids having to deal with the so-called hassle of which style guide to follow when it comes to title case.
However, every major style guide I can think of advocates for a specific title case scheme where some words are all in lowercase. They don't necessarily agree with each other on exactly which words should be in lowercase, but they do all seem to agree that some should be. (I believe every one I've read indicates that articles and conjunctions should be in lowercase unless they form part of a proper noun or are the first or last word; it's the prepositions that end up in a grey area.)
Incidentally, here is Merriam-Webster's definition of listicle:
: an article consisting of a series of items presented as a list
// Even in the well-worn format of the listicle, Ono infuses her characteristic verve into this list of 25 facts about herself.
— E. Alex Jung
It's a real word, so you don't need to put it in quotation marks. Neither in that definition nor in any other discussion of the word that I've seen do I find any reference to every word in a listicle item's introduction having a capital first letter. Nor have I found that mentioned in discussions about bullet points and list items.
At most, I see references to title case—but all in the same way as the various style guides that would have you leave some words in lowercase.
So, while you may be able to point to some examples of listicles in which the first letter of every word in an item's introduction is capitalized, it's purely a matter of style and subjective use rather than any kind of universal rule.