I can venture a guess. They replaced the Disney Springs Vinylmation store with a Star Wars store. So, in the year or two leading up to that change, they must have already known they were rebranding that space and wanted to phase it out. Plus there are now Pop! Vinyls which is more competition. And perhaps they already issued as many Vinyl themes as they felt they could, they still have some Vinylmations for sale, but no where near the amount they had before. There was also more costs involved with the trading, they had to have mystery boxes in multiple locations and labor involved with trading that wasn't necessarily driving more sales and probably clogging up sales lines. I also heard people were going into the Vinylmation store with pocket sized scales and they were trying to scam the system by figuring out which box had the "chaser" which was more valuable than the rest, I'm sure they didn't stop over that, but that sucks.
It was a huge bummer, I really loved trading them, it was more satisfying and exciting than pin trading.