When you need to express that a situation is caused by multiple factors, you can use a variety of synonyms for "due to a combination of causes." One option is "attributable to a complex interplay of factors," which emphasizes the interconnectedness of the various elements contributing to the outcome. Another possibility is "resulting from a confluence of factors," which suggests that multiple streams of influence are converging to produce the observed effect. Finally, "stemming from a blend of factors" emphasizes the mixture of different ingredients that have come together to shape the situation at hand. Whatever the phrasing, using multidimensional language can help lend nuance and complexity to your writing.