In principle whoever is building the Android system can choose whatever roots they want. In practice the Android Project is a Google project, and follows Google's policies.

Also in practice, Google's policies strongly resemble Mozilla's. Mozilla's root programme is overseen by mozilla.dev.security.policy, a public group. So, to some extent the answer to "Who governs that list?" is you do, much as (if you live in a democracy) it's your fault that your government is terrible. You could work hard to improve things. But, you probably won't.