Disc brake equipped time trial bikes in grand tour Why did team Deceuninck–Quick-Step ride disc brake equipped time trial bikes in a relatively flat course through Brussels in stage 2 of the 2019 Tour de France?
The main reason is the 2020 Specialized Shiv provided by their sponsor is only produced in a disc version.

You can see an article about the bike here:
https://www.bikeradar.com/news/specialized-sworks-shiv-tt-disc/