Re: I'm baffled
With mobile app voting, you will not get a validated statement of how you actually voted, so you will be unaware of any fraud, and have no ability to raise a dispute and have the vote corrected.
It might be worth noting that there are protocols for voter-auditable secret-ballot voting, such as Rivest's ThreeBallots. The problem is that they're hard for many voters to understand, and increasing the cognitive load or work factor of voting even a little will have the effect of suppressing some of the vote, when participation is already pretty dismal.
The fact of the matter is that mark-sense paper ballots with privacy-protected in-person voting where possible is still the best overall compromise anyone's come up with so far.