They haven’t updated it - I made a Twitter post explaining this (linked below), but essentially:
The ‘too blue’ screencaps are from a 4K HDR blu-ray: HDR colour data doesn’t translate to non HDR screens, which gives them sickly or faded colours. The source of these screencaps are the first Google result for ‘The Rise of Skywalker screencaps’, so people who (for whatever reason), haven’t watched the movie since cinemas (and have seen these images widely-circulated) will give it another go on Disney+ and assume it’s been re-graded.
Comparison pics are in the tweet: https://twitter.com/ChrisRogers1138/status/1397251817638187010