Do you understand the difference between proportional representation voting vs. non-PR voting?
"Democracy is a form of government in which all eligible citizens have an equal say in the decisions that affect their lives. " - Wikipedia
A republic isn't by default a democracy. Non-PR voting doesn't allow all citizens to have an equal say because their vote doesn't count if they vote for smaller political parties; At minimum it's not taking away seats from other parties, and not showing the genuine support for smaller parties -- and the bigger political parties know this and is why they want to keep the system this way.
"Democracy is a form of government in which all eligible citizens have an equal say in the decisions that affect their lives. " - Wikipedia
A republic isn't by default a democracy. Non-PR voting doesn't allow all citizens to have an equal say because their vote doesn't count if they vote for smaller political parties; At minimum it's not taking away seats from other parties, and not showing the genuine support for smaller parties -- and the bigger political parties know this and is why they want to keep the system this way.