Because 99% of the time, the site doesn't list wrong-back errors: https://www.tcdb.com/FAQ.cfm?ITEM=WrongBacks
If it's unintentional, and the process happened like the FAQ item linked above describes, they wouldn't get listed. This seems possible, since it's apparently all the same cards that are affected (meaning that it could have been the same series of sheets that this happened to).
If it's intentional, and Topps intends for these cards to be considered unique collectibles, then they would get listed. This also seems possible because Topps.
Now, we also need to be conscious of the fact that if they're unintentional, but wide-spread enough, Admin may make an exception to have them listed. He has done so before with certain errors that aren't usually catalogued here (I wish I remember what set it was, but there was a late 2000's Topps baseball insert set that had a ton of foiling errors, and it affected most, if not all, cards in the set. Admin granted those an exception because of the mass production of them).
I haven't revisited this for a while. Has anyone seen confirmation from Topps and/or a hobby source that these are intentional? That would be a good starting point. Not a forum thread or eBay results, but actually from the manufacturer themself? Last I looked, I hadn't. I wouldn't necessarily trust a customer service rep to be in the loop either, honestly.
I'll never quit collecting entirely, but I am downsizing. Check out my COMC store and help me thin out what I don't want so I can buy cards that I do want. See something you like? Send me a message on here, and we can knock the price down quite a bit. I'll even take a bit of a loss if it means getting you a card you really want.