Why can a disjoint event not be independent?
That is because you know one event will happen when the other doesn't, which means they are not independent- outcome of one DOES influence or affect other outcomes.
Two events (let's say A and B) are disjoint (also called mutually exclusive) if they have no outcomes in common and never occur simultaneously.
Therefore, if event A happens, you know for a fact that event B will not happen.
Hope this helps!