Banning the cards really hurts no one, since they're all fringe playable at best, and makes a portion of the playerbase more comfortable in the community. Seems like a no-brainer win-win to me. Obviously there is a financial motive on WotC's part, but their heart is in the right place too, I know and work with a lot of these folks and this really did come from a good place.
That said, I definitely had to have a few of them explained to me, but they all make sense after that:
Invoke Prejudice: Obviously KKK imagery, from an avowed and vehement racist, with 1488 (a neo-nazi dogwhistle) as its gatherer number. Ouch.
Cleanse: A white card (ok). That destroys black creatures (ok). Named Cleanse (...ok?). Ethnic cleansing (oooooooh).
Stone-Throwing Devils: Apparently an old middle-eastern pejorative, and once you know that the art is super obviously a racist caricature.
Pradesh Gypsies: 'Gypsy' is basically the N-word for the Romani people. It has been appropriated to mean something fairly benign in modern media, but its roots are that of baseless bigotry towards an out-group. A lot of folks with that heritage have repappropriated it and use the word proudly, but at the same time a lot of folks still find it offensive.
Jihad: Name and art reference real-world racist, violent religious war/massacre. Let's not do that.
Crusade: Name and art reference real-world racist, violent religious war/massacre. Let's not do that.
Imprison: What appears to be a starving black man in a torture mask, with a card name that sniffs of slavery.
Both Cleanse and Imprison are a bit of a stretch, but honestly they toe the line enough and are unplayably bad enough that it feels free to axe them just to be safe.
Speaking to the newly found value of these cards, its a temporary bubble with two types of people participating. 1) Speculators who knew that the banning would spike interest due to FOMO, and 2) Actual full-blown racists who want to collect and protect racist iconography. Eventually the price on these will go back down as folks lose interest, and we'll be left with slightly richer speculators and slightly poorer racists, so it all works out. Invoke itself may very well hold its price, since it is the rarest of them and holds a sort of freak-show novelty, but the rest will absolutely fall off a cliff and take a lot of stupid peoples' money with them.