The $800 was for a different deal. Your seat in trade for an $800 voucher and a different flight. They deemed you to be not eligible for it so you could not give up your seat. And if your replacement flight had a mechanical, you'd be entitled to another voucher even though you had the $800 for a VDB.

I believe Southwest is recently cutting back on the vouchers. Why do I suspect this? The new official boilerplate on voucher requests is quite strict now. One request. There is no place for verbiage such as sleeping at the airport or other explanations. Once you get a voucher, you can't get another one for the same delay. You could try to test the boilerplate for the rest of us to see if you can get more after already receiving that paltry $100. But temper your expectations too. You're not getting $800. I sort of understand why Southwest doesn't want sob stories anymore. AI can generate some really good sob stories that would be worthy of $2000 vouchers and creative writing awards.

If I was at least 99% sure this was mechanical, I would have stayed at the hotel, saved all the meal receipts, and gambled on a near 100% chance that Southwest will eventually reimburse me.