There's a million reasons based on the website and content structure.
Your homepage could get more traffic because of brand queries, while a specific content page gets more leads because it's got content that is more relevant to the user.
Alternatively, a high traffic page might make it difficult for someone to become a lead (e.g., no forms, or the form is hidden) while a less trafficked page makes it easier to submit the form, above the scroll.
Traffic != more leads. A low optimized but high trafficked page isn't going to fare better just because you throw more traffic at it.