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).
$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.