The problem is that it solves a problem that nobody actually has and provides tinder to make a problem that actually exists worse.
Political machines exploiting nursing homes, pushing absentee ballots on the elderly, etc are already problematic, and allowing field GOTV teams to collect this type of data in mass is would make expanding these operations in size and scope.
You’d also create the new problem of hyper-partisan people crying about voter fraud. You’ll have a bunch of lunatics running around with fake ballot receipts to push whatever narrative they are trying to push.
In my state, it’s illegal to take pictures of ballots at the poll, and there are bipartisan poll inspectors that will shut that down if it happens.