A word that defines when you have to consider multiple factors when making decisions
I suggest dropping the isn't and describing what it is. With the isn't, a reader will have to infer the opposite of the adjective you use. I propose
multifaceted
having many facets (see FACET sense 1) or aspects
a multifaceted approach to health care m-w
facet 1: any of the definable aspects that make up a subject (as of contemplation) or an object (as of consideration)
Each facet of the problem requires careful attention. m-w