Moreover, backing or tying a cryptocurrency to another asset requires a proper valuation (and ongoing revaluation) of underlying asset. That is difficult and for example banks employ large teams to do it.
And even if such audit takes place doubts will still persist, this is what happened to tether some months ago when people began to worry if all the tether in circulation was in fact backed by dollars, everyone in tether backed their claims and said there was nothing to worry but I do not remember if an external party was given the chance to test if their claims were true so trust will always be an issue with such a coin.