My guess is because people fundamentally understand that getting something for doing nothing (i.e. redistributing the new coins based on share of the collective) is communism.
People actually do something to get new coins. As Sunny King has said if my understanding is correct, keeping coins to get coins is actually "saving". You lose the ability to spend your coins in exchange for having more coins in the future. Well, if that is communism, then I'd rather have that than see unproductive capitalism. Imagine a third world country entrenched with capitalism spending resources on mining hardware and energy rather than agriculture, infrastructure, or whatever just because it is more profitable. It just doesn't make the world any better.
Also PoS does nothing to help you get your initial coins without a fiat exchange. And you can't increase your share by being more proactive, innovative, and risking your capital on mining.
Without risk, no new knowledge is created. Ponder that.
You could always trade physical goods get your initial coins. It brings REAL world innovation. A person could do or produce something innovative and ask for coins. The coins become an asset that generate recurring income. I'm not quite sure about the "risk" you are speaking of but people use a currency because they TRUST it. People use fiat currency because they believe that the risk is so low that it is worth representing value. When there is risk that the USD, for example, would collapse, people stay away from using it. Therefore, when there is less risk, the currency has more value. I think PoS coins haven't caught up yet because people aren't aware of it yet. I feel that the transition would be mainstream fiat currency to BTC then in the long run BTC to PoS coins but I may be mistaken.