Why wasn't the USSR more democratic

wouldn't the paris commune literally count? If not then democracy was a fairly common form in primitive communism.
Almost no one who advocates for democracy thinks this, so that's the argument you should be having.

"Increase democracy" means increasing the amount of control the proletariat has over society.
It means things like the proles owning the means of production and them bein able to better hold their representatives accountable.
It means we extend democracy into the economy more and we improve what democracy means.
Etc etc.

...

Pirates.

All power to the Soviets and a one party organization is not mutually exclusive.