Then that commission was either deliberately oblivious or lying.
An example of that would be the dual state registration and mail exchange scheme. This one happened for real between about a dozen people each in Ohio and Arizona about two decades ago now.
What they did was all were registered to vote in both states as there was no cross-check on registration so neither state knew they were. They elected to get mail in ballots. All 12 (or whatever) were sent to one address that all of the participants in the other state were registered as their home address in that state. The person that was key in each state then sent the ballots for the other state persons to them via fed ex. They were filled out, returned fed ex, and then mailed in from the appropriate state location.
The scam only became known because someone checking the voter rolls thought it was strange that 12 people all lived at the same address, a small house. It unraveled from there.
If voter rolls aren't being checked purged regularly as the Democrats want to have happen, that would make the above virtually impossible to detect.
When the ballots are out of sight, and there is weeks of voting time involved, such schemes are doable and virtually undetectable. Yet, your claim is because it hasn't happened (that we know of) it can't happen. Well, it can and it likely does.
Vote pairing or swapping, is a questionable but legal variant of the above.
https://mashable.com/article/people-are-trading-votes-and-its-legal
The only sure way to ensure clean and open elections is in-person voting with ID and careful checking for validity on an election day at a polling location where everything is under surveillance. Mail-in voting, especially when coupled with all the stuff I mentioned, is nothing but a mass fraud possibility one election away.