Why isn't simulfrac and trimulfrac used all the time?

I'm not as familiar with the unconvetional space, coming from conventional/deepwater and had a question about simul/trimulfrac.

My understanding is that these methods are better than zipper frac since they work on the wells 2 or 3 at a time. However, if that is the case, why is this not used in all current frac jobs? What role or benefit does zipper frac still have?