CGC doesn't sell trust. They sell an evaluation, and they make the rules by which that evaluation happens. It's up to us to buy into their rules, and judging by their wait times, they've had plenty of buy in.
If they're not selling trust, what are they selling? Trust in their grading ability. Trust in the impartiality (not grading certain people's book more favorably). Trust they won't damage your book. So on and so on.
They're selling an evaluation that most of their customers rely (wish?) on to make money. It isn't about trust. If it was trust, then they'd grade strictly, not loose enough to get max value out of a book. CGC isn't in business to give collectors trust. You'd like that to be the case, but it's just not their business model. Just look at their advertising (Your book is worth 10X more in a CGC slab!!!) They are in business to make money, and the best way to do that for this market is to tantalize others with the opportunity to make money.
Actually, you just gave me an idea, Dan...99.8 percent of my collection is not slabbed/pressed etc...maybe I should start selling more books...they will all have POTENTIAL:) :
Sadly, this is what the most publicly visible portion of the market has become.