You're worried a powerful person will buy votes from a small, apathetic minority. But mandatory voting makes that problem worse, not better. If you force everyone to vote, the rational move for someone who doesn't care is to sell their vote to whoever pays, or copy whatever ad they saw last. That's just adding more uninformed, easily-manipulated players to the game. The powerful man doesn't need a majority, just enough confused votes to tip it. Low turnout is a signal that people aren't engaged; forcing false participation doesn't create real accountability, it just lets the manipulators farm it at scale.