Edit to add: they made me this offer at the airport kiosk, immediately before my flight boarded. They knew it wasn't anywhere near full.
An optional fee for priority boarding is very different. (I don't understand the folks who want to rush onto the plane to sit in a less comfortable seat, but that's a different issue entirely.)
The post you're responding to is essentially a complaint that they purchased insurance (at a known negative expected value) and didn't see a payout. Which on its face is ridiculous.
It doesn’t happen often but checked bags can get lost. Also, waiting 10~15 minutes to pick up your bag can be annoying after a long flight.
If you fly American a lot, the branded credit card is the way to go. Not sure if the same is true for the other carriers, but I'd suspect it is. Even with the most basic economy ticket you get most of these optional add-ons (one checked bag, better boarding position, select your seats) as a cardholder. Credit card spend also counts towards status qualification for AA now, so CC spend can get you across the line to gold status if you might not have made it otherwise, and at that point you'll start to get upgrades to business/first on flights where everybody on the plane doesn't also have status. That will put you in boarding group 1, which, hey, mission accomplished and you didn't even need to spend $29 at the kiosk :).
Stats don't lend themselves to perfect predictions.
Most of the time, there's somebody who's happy to have the free travel. I've done it and the compensation was approximately one free transatlantic round trip in exchange for spending the night in an airport hotel. The cost to the airline is, of course not the face value of the voucher.
To put a finer point on it, I wanted to get some value out of my $29. I got none. If I said "Hey, give me $29. I'm not gonna give you anything, I just want $29," would you give it to me? Transactions in capitalism are supposed to be voluntary, mutually beneficial exchanges. What benefit did I get? AA exploited an information asymmetry to scam me out of $29.
It's not for sellers to make value calculations for buyers. Caveat emptor.
But, here, they clearly exploited an information asymmetry to make me a zero value offer, knowing there was some probability I'd accept. Caveat emptor only applies when you have some way to evaluate or vet the offer in advance. With the hidden information that was kept from me, I was robbed of such opportunity.
Would you be complaining if the entire flight was full of people in group Z (for some value of Z < X)? Or if you'd bought a day-of-travel upgrade when you would've gotten a complimentary upgrade with your frequent-flyer status? Or if you'd paid extra to select a seat at booking when the seat you wanted turned out to be open at check-in time? Or if you paid to change your flight rather than wait on free same-day stand-by?
For all you, or the checkin agent, know there could've been irregular ops that moved the entire passenger complement from another flight to yours after you checked in. Unlikely, but it happens.
If you're really that worried about, write the airline and complain. They may give you a refund or some free miles or something. However, you got exactly what you paid for and entered willing into the transaction.
And, to be clear, literally the entire business of airlines (which is yield management) is based on asymmetry of knowledge between between travelers and carriers.
You knew the service, the possibilities and everything else.
Stop complaining.