If you want to think of propaganda in terms of advertising, it's sort of judgement advertising. Doesn't really matter who pays for it. The purpose is to not let people make their own judgements on certain things. While the purpose of advertising products is to inform public about existence of products. Using propaganda in advertisement is usually illegal too.

>the purpose of advertising products is to inform public about existence of products.

Really? It's not like any of us don't know of the existence of Coca-Cola; I think that the vast majority of advertising we encounter on a daily basis is for products we know about already (even though this is probably less true now than it was towards the beginning of my life.)

> Using propaganda in advertisement is usually illegal too.

citation?

Grandfather Frost, to be pedantic.

Even in Soviet Union no one would bother to print post cards that no one will buy. So these are of popular demand at that time.

That could also be explained by there not really being many other options. I don't think too many people really wanted to send postcards with Lenins and red flags for holidays, but if this is all you have, you'll buy that.

By a similar token, Brezhnev's "memoirs" (Малая Земля etc.) were published in millions, but I have never heard of anyone who wanted to buy, let alone read them.