The middle class has a strong incentive in ensuring good governance as they depend on public services such as public schooling and transportation. A failure to invest in the middle class by non-democratic states will likely lead to calls for reform and better governance.
Middle classes tend to demand regulations, the fair enforcement of contracts, and the rule of law more generally—public goods that create a level social and economic playing field on which all can prosper. Arbitrary despotic rule often does not allow for this.