St. Ann's Warehouse leaving empty seats at Oklahoma?

I can't speak to their accommodating people on the waitlist line, but I remember staffers moving people who were in the last row in what looked like obstructed-view seats into empty seats that were in better locations, so maybe they prioritize moving people who already have tickets into the good (open) seats and just cut their losses and leave the unsavory seats open.

Unless they have a strict policy against seating latecomers, I'm not sure how this could be handled. I think a handful of people entered a few minutes late when I saw Oklahoma.

Oh, I thought they didn't have late seating. They had no late seating for another show I saw there, so I thought it was their universal policy.

As others have said, it is against the law to sell the same ticket twice --- the empty seats were no doubt "no-shows".

It breaks my heart, but a theater I work at frequently has this problem. The show is sold out, but there are a number of empty seats due to no-shows.

And legally you are restricted from selling a seat that is already sold.

In the old days, before online sales, small theaters took reservations rather than sales. A reservation could be released if they were a no show. But if payment has been made there are restrictions.

I've managed box offices for 30 years. You cannot sell the same seat twice, under any circumstance. Regardless of whether you have late seating or intermission or no-shows. Ticket selling software does not allow you to sell the same seat twice. It's set up this way to avoid seating conflicts where two people have a ticket for the same seat. It's also to prevent embezzlement.

Once you sell a seat it becomes unavailable in the system. The only way to make it available again is to refund the first sale. And you can't always do that since the no-show may have paid in cash. Also theatres have no interest in doing that because they've already done their job by selling it once. Why would they do double the work to sell it again, and all at the busiest time of their day, show time.
The only options remaining are to either let the people waiting in for free or to sell the seats outside of their ticketing system software. I guarantee you that reputable theatres aren't going to do either of these and could get in big legal trouble for doing the second, which is tantamount to selling under the table.