One reason could be that Starfire is simply learning the language, so her Spock Speak is because she's not comfortable enough speaking in English to use contractions, natural slang, etc. Another theory is that she is implying Tamaranean speech patterns to English (i.e., in Tamaranean, all nouns or names must be preceded by the equivalent of "the", hence her tendency to use "the" before all nouns and names).