Why were many eastern countries considered to be ruled by puppet regimes after world war 2?

Puppet State is a concept to explain a state that is independent but in fact is dependent upon an outside power for numerous reasons such as financial interests, economic or military support.

After the WWII the Soviet Union acquired many puppet states such as Tuvan, Lithuania, Latvia, Estonia, Azerbaijan, and others.

The Soviet Union gained control over those puppet states during the Baltic Operation in response to an offensive launched by the Nazi army. These countries could vote but they had no choices, the only party to choose from was the Communist Party and other parties were outlawed, citizens were not allowed to complain about this one-party system.