Those movies are nearly 10 years old and approaching obscurity via zero merchandise sales. In fact, it seems odd that Chapek would approve Rat for WDW for the same reason. I can only assume the cost savings of cloning from Paris factored into the decision.
Although it's virtually non-existent at DLR, Ratatouille actually does pretty decent merchandise sales in Epcot. If I had to guess, I would say it's probably the most popular character-branded merchandise in World Showcase. Remy has also been featured on the park's annual International Food & Wine Festival merchandise (with strong sales) for several years. I think it helps that within WDW Ratatouille merchandise can only really be found at Epcot, so there's some exclusivity and uniqueness, and it's a film with more adult themes while still being a cute-and-cuddly character, so it can appeal to a broader audience than something like the Princess line. Remy is definitely not an A-lister, but he performs solidly and consistently
At DLP, Ratatouille merchandise is incredibly popular. The film always resonated with French audiences, and now with the ride and restaurant, merchandise flies off the shelves. DLP and Epcot's France pavilion already share a lot of co-branded merchandise (or similar designs with label changes for their respective parks), so I expect a lot of the Rat merchandise will make its way stateside
But one of the biggest reasons that Ratatouille was chosen wasn't the merchandise opportunities or the cost savings in copying the design (which frankly is minimal compared to the construction costs), but the time savings in having a project that is ready to go. Similar to the trackless Mickey ride, WDW wants to use the attraction as counterprogramming against Star Wars, and needs it to open at roughly the same time in order to disperse crowds.
The location in the France pavilion makes it an even more appealing option, since International Gateway is easily accessible from the Studios. It will also help create a draw to Epcot while all sorts of other projects take place around the park, similar to how World of Color helped pull crowds to DCA during its redo. Although other options were considered (including a Beauty and the Beast ride similar to what Tokyo is getting), they went with Ratatouille because it could be done quickly; they need this thing open yesterday.