Why Title Case Capitalized Words It Shouldn't Have
Standard title case rules typically leave short articles (a, an, the), coordinating conjunctions (and, or, but), and short prepositions (in, on, of) lowercase unless they're the first or last word of the title — a converter that capitalizes every word regardless of length or part of speech is using a simpler rule set than the conventional style guide approach, which can look wrong to someone expecting standard title case rules.
This is a common point of confusion, since "title case" isn't a single universally agreed rule set — different tools and style guides handle short words differently.
The standard rule for short words
Conventional title case rules (following most major style guides) keep short articles, conjunctions, and prepositions lowercase in the middle of a title, while always capitalizing the first and last word regardless of length — "The Lord of the Rings" follows this pattern, with "of" and "the" lowercase in the middle but "The" capitalized at the start.
Why some converters capitalize every word
A simpler implementation that just capitalizes the first letter of every word, regardless of the word's length or grammatical role, is easier to build but doesn't match conventional style-guide title case — this produces a result like "The Lord Of The Rings" instead, which looks noticeably different to anyone familiar with standard title case conventions.
Checking which rule a specific tool uses
A well-built title case converter typically offers a choice between style guides (AP, Chicago, or a simple "capitalize everything" mode) — checking which specific mode is selected explains a result that looks different from what standard style guide title case would produce.