Quite the opposite. All of the fraud takes part completely out of sight of any control. The ballots are mailed out to addresses the fraudsters know they will be coming to. There's no control on the receiving end so it's easy for the fraudsters to collect the ballots. There is ZERO way to know who actually filled out such a ballot. If a signature on the envelope is the only control, and almost any signature is accepted, that too is no control.
Add ballot harvesting, drop boxes and up to a month period for voting--along with counting late ballots-- and you have a perfect storm. A fraudster or team of them could collect, process, and deliver thousands of fraudulently cast ballots with no means of being caught other than one of them admits to the crime.
You could even break up the work to get more ballots done while making most of those involved think they were just doing something legal to begin with. The collectors are simply persons at the mail receipt location that get all the ballots as they come in, like a nursing home. You have one operative there that collects tens of ballots meant for the residents who are incapable of voting being senile, insane, comatose, or otherwise incapacitated but on the voter rolls from a time when they weren't. These are handed to a mule to turn in to the vote mill where a few (at most) trusted people fill them out and prepare them for delivery. Another mule delivers them for pay.
The mules think they're just legal, paid, ballot harvesters as allowed by law. The only people in the know on the fraud for sure are those filling out the ballots. They have several weeks to do the work so they could turn in upwards of thousands of fraudulent ballots.
Without mail-in elections, without weeks of voting, without lax ID requirements, without ballot harvesting allowed, this plan falls apart. If you have to vote in person, have to show ID, then such a scheme doesn't work.
Other nations know this and that's why virtually every nation on the planet severely restricts or doesn't allow mail-in voting.