Which factor is not typically considered when evaluating text complexity?

When evaluating text complexity, one of the primary considerations is how well the text engages readers at various levels of understanding and skill. Thematic depth, syntax, and vocabulary are essential elements that contribute significantly to how challenging a text is. Thematic depth refers to the intricacy of the ideas presented and is crucial in determining the richness of the narrative, which impacts readers' comprehension and engagement levels. Syntax and vocabulary play a significant role as well, as more complex structures and advanced word choices can elevate the difficulty and influence how readers process the information.

In contrast, while illustrations may enhance a text's appeal, they do not typically affect its complexity in terms of the language, themes, or ideas presented. The presence of illustrations can aid comprehension for some readers, particularly younger audiences or those who are visual learners, but they do not inherently alter the fundamental challenges posed by the text's content. Therefore, illustration frequency is not a primary factor in evaluating text complexity, making it the correct answer to this question.