Offer me some cold, hard cash, and that would completely change the game. I have, very rarely, seen airlines resort to that if the vouchers don't do the trick. I'd be utterly shocked if an offer of $800 cash couldn't produce four volunteers on a fully loaded plane.
This is wrong. By Department of Transportation rules, the airlines is required to pay up to 400% (max of $1,300) for an involuntary rebooking that results in a two-hour delay or more. Airlines might try to get you to accept less by offering voluntary rebooking for less, but if they bump you involuntarily, that's what they're required to pay, and it's not sufficient to offer only a voucher with restrictions.
European airlines pull the same sorts of tricks to try to reduce the amount that they pay out, or to get travelers to accept vouchers instead. It's not limited to the US.
$800 round trip is like Boston to Hawai'i next week.($822 from next monday to the 1st of May). That's 8,081km/5,021 miles. It honestly wouldn't be that bad.
I found the flight you're looking at:
" Chicago to Louisville O'Hare Intl. (ORD) to Louisville Intl. (SDF) American Airlines 3520 operated by Envoy Air As American Eagle Economy / Coach (V) Canadian Regional Jet 700 "
V class is "Discount Coach". (http://www.cwsi.net/united.htm)
Only full-fare refundable ticket classes are eligible for voucher use. In essence, "Y" class: "1st Tier Economy. Full Fare unrestricted coach class".
In fact you couldn't fly ORD to SDF at all on a voucher because every seat on the "dba Express" carrier flights are "Discount Coach" or "Deep Discount Coach".
If anything, this proves my point. Because an $800 voucher sounds great, until you realize this.
Your other example?
https://www.expedia.com/Flights-Search?trip=roundtrip&leg1=f...
No, you're looking at $2,600+ for BOS-KOA return that's eligible for voucher use (not sure if you can use a voucher as part payment).
In the US you hear "offered $800 compensation". It's not cash. It's a voucher for use only on that airline, only within 12 months, and only on select full-fare ticket classes. So an $800 ticket may only get you another round flight from Chicago to Louisville (around 500km/300mi).