i'm not sure i completely understand the strategy - actual official drop boxes are pretty abundant and easy to find, so i find it a bit hard to believe that they think they can increase turnout by making collection more convenient.
the idea floated by rouda (that they'd "lose" ballots from dem voters), is entirely plausible. obviously that's sort of assuming the worst, but, i mean, they are illegally collecting ballots. there's not a ton of innocent explanations for that.
it could be more benign. like, data is important to campaigns. just collecting the names of voters that have already cast ballots so they could cross them off their contact list and focus resources on voters that hadn't voted would have some value.