@ClayShentrup has provided some relevant research links in: Approval voting vs instant runoff voting, condorcet, etc
Apparently (based on Clay’s summary) the evidence that the preferential voting systems actually capture preferences better than the simple two level “more preferred”/“less preferred” mechanism used in approval voting isn’t that strong, so it’s hard to justify their complexity when approval voting is easier to explain and resolve.
Maybe the fact approval voting lumps +0, -0, and -1 votes into a single “not approved” category is a feature rather than a bug to be fixed?