“We recognized that there was not an easy way to gain Bitcoin exposure, so we’re trying to creating a simple solution,” Tyler Winklevoss said in an e-mailed statement.
That's the whole deal, pure and simple. They are aware that the effort to buy and hold bitcoins today is much too difficult, and could be simplified. An ETF does that.
Also, they might have added ... if the U.S. banking system didn't suck so bad (high bank wire fees, slow transfer, anti-fraud holds, bank holidays, etc.) then there would be less of a reason for this ETF to exist. But it is what it is, so there is room for an ETF.