The biggest shift in the past ~100 years or so was the fact that mass-literacy became a thing. People started writing how they speak.

The written language's disconnect from the spoken language had a bunch of different reasons: bridging the gap between mutually-unintelligible regional dialects, political gatekeeping, etc.

I think the main claim of "Modern Chinese can read as English in Hanzi camouflage" owes a lot to the fact that they're two "subject verb object" languages with similar formal/written registers.