Archaeologists will change a theory based on a new find. So will Historains. So will Scientists
The key word there is "new", something they hadn't seen before, or as in the case of scientists, maybe something not previously invented.
The watchtower, on the other hand, claim to follow the bible as their textbook. There hasn't been anything new in there for 2000 years. As for the bs the wts spew out about "progressive understanding", that's just an excuse to change a doctrine when the sands of time run out on it, as with the generation idea that they had to abandon in 1995, before all those around in 1914 died off.