Because authoritarian regimes and price controls are two sides of the same coin.
Economic power == political power
By ceding economic power to the public to kickstart their economy, authoritarian regimes would be ceding political power.
In contrast, by implementing price controls and vouchers/subsidies, they place the government in charge -- only government-permitted economic activity exists, which prevents people from gaining power themselves.
To those regimes, scarcity is preferable over price increases. Scarcity makes everyone grumble, but allows winners and losers (via the government choosing). Price increases just make everyone grumble and realize how poor they are (internationally speaking).
Or in summary, you're optimizing for efficient economic activity.
They're optimizing for regime stability and survival.