Honestly, in hindsight it's kind of crazy that Splash lasted as long as it did. A ride based off of a movie that Disney has actively tried to bury for over 30 years now is not a great look. It's a testament to how well-made the attraction is that we have people defending it in the first place, defending it as if it was a classic attraction that Walt would've scribbled down in his plans for Frontierland 1.0. It's easy to forget that this was a ride built in the 90s, about 40 years after Song of the South released and quite a bit into the backlash period. It was always kinda fighting back it's source material with the name change from Zip-A-Dee River Run into a reference to forgettable Tom Hanks vehicle Splash and the ride design purposefully leaving out any trace of the Live action elements from the movie. Disney's silent erasure campaign against Song of the South making sure that the vast majority of guests would never even know about the movie, with the helpful plus that most of the ride is generally Disney-y enough for people not to think too much about the theming helped immensely. But I think it was always a balancing act, and one I can't imagine Disney wanted to do forever.
That's why I honestly don't think this decision has much at all to do about the social movement. I can imagine Disney saw the writing on the wall for Splash a long time ago, and I think some parts were probably actively hoping for the change. The ride system itself is so popular, and especially in the summer, so essential that they must've realized what a missed opportunity it all was. You can't sell excessive amounts of plushies or mugs of characters people know nothing about, but you can't just tell them to watch the movie because you definitely don't want them doing that either. Brer Rabbit or Brer Bear were on the tier of Figment or Orange Bird, but I don't think that popularity quite matches that of true IP characters.
I absolutely believe them when they say they've been working on this for over a year, if only by technicality. There are probably a thousand ideas sketched up in their offices that we'll never hear about and will never see the light of day. I'm sure some Imagineer at some point has thought about the dilemma of basing your most popular ride off of your most infamous movie and come up with a couple of ideas for replacements if things get nasty. It just so happened though that Splash was still just as popular as it had ever been, and they had enough big projects at the time to push off the Splash re-theme for a rainy day. Then this whole thing happens and shines a harsh spotlight on Splash's flaws and Disney decides to finally rip off the band-aid and take the technically-a-year-in-production Frog retheme off the backburner. I can't agree with people who view this situation as simply a righteous movement finally getting through to big evil corporate Disney or an angry mob taking away their favorite toy, I think it was just people giving Disney enough motivation to do the thing they've actually wanted to do for ages.
Hoping this take doesn't come across as too 'galaxy-brain'-y or whatever, not my intention. I just don't trust Disney to fully mean what they say when it comes to the whole social justice thing. Follow the revenue and see where it comes from. It's hard for me to think that some part of Disney didn't resent the fact they couldn't make more money off Splash while they could. Song of the South was universally a bad look. Frog is a much safer bet for them, even with the Voodoo or Witch Doctor stuff.