No miracle about it, Jungle Cruise only received an update because they were in desperation mode trying to purge the perceived "problematic" elements of the attraction.
Big Thunder has little to nothing that would be found to be problematic. Perhaps someone might harp on the backstory a bit involving the Native American legends, but that would still be a pretty major stretch even for their absurdly obsessive committees (it's really just one small line of dialog on the riverboat as well).
I doubt WDW's Big Thunder will ever be updated at this point. The ride is in pretty horrible shape too and desperately needs a massive at least 1+ year overhaul. Nothing has moved in the flooded town scene for a few years now. Last i rode it, almost all of the bats were either static or missing, and the waterfall at the top of the first lift was broken. And yeah obviously the complete lack of anything in the third lift for well over a decade now. The ride has also become outright painful due to desperately needing a full track replacement. Something I believe every other version of the ride has already received over the past decade (at least California and Paris, not sure about Tokyo).
