As suggested, this question is actually aconcerns MetaSE question, so after some research I will self-answer it. There are indeed some answers to this question in MetaSE: Why do we need multiple approvers for suggested edits? The reason summary was given by another comment in duplicate question of mine by @Spevacus:
The TL;DR is... Quality. It's extremely easy to hit "Approve" on an edit that might not be that great of an edit. It's less likely that two people robotically click "Approve" on a bad edit. It's much less likely that someone hits one of the improvement options and actually makes changes themselves and those end up being bad changes.