Only a fraction of the entire Steem supply is pegged by SBD. But it's enough to put pressure on the price. If the community could maintain the peg for the amount backed by SBD, then the price of Steem itself should be much more interesting.

Think of SBD like some kind of "vault". Not all the people will keep their assets in a vault, but those who are keeping it, they want the vault to be impenetrable. That's the role of SBD and that's why it doesn't peg the entire supply, leaving the majority of it freely floating on exchanges. So the comparison with Swiss Franc only holds to a certain point.