Not all countries have the medallion system (or that system the way it works in parts of the USA), and in some places drivers felt they were paid pretty adequately the way things were, and so they reacted very negatively to Uber drivers showing up and undercutting them.
In places where medallion or similar systems were in place, most of the protesters tended to be medallion owners. Who may or may not themselves be drivers, but even if they were were probably still deriving significant income from non-owner drivers renting their cars and medallions.
