Tbh it doesn't really make sense to me to axe this feature of quick swipe.
Using multiple watch faces and customizing the watch with them always felt like such a core concept of the Apple Watch. And with each release, even the latest watchOS Apple added new watch faces like the Snoopy, which feels like a clear hint that most users would switch between watch faces often through out the day (Snoopy is nice and fun, but barely useful for anything than reading the time, so I'd switch back and forth between this and at least 1-2 other faces all the time). So why make this harder and less intuitive?
Also, suddenly after 10 years of watchOS Apple realized accidental swipes are a huge UX issue?
I wonder if the real reason could be a system resources issue due to massive changes on single watch faces consuming greater amount of resources. And they disabled fast swiping kind of last minute to avoid bad UX due to lags & stutter.
Even when my Series 7 was brand new I sometimes noticed quickly swiping through several watch faces causes small amounts of stutter in animations and at times watch faces even needing some longer time to load. But most of the time this wasn't an issue, esp. not when just switching between the same 3-5 faces all day long.
However, with all the redesign work, perhaps watchOS simply ran out of resources when fast swiping? And disabling the feature was like a last resort solution. The extra steps of user interaction to send a watch face in the background, swipe through non-interactive thumbnails then tap to activate the final face, certainly buys watchOS more time to freeze and store a face, then load and restore another and clean up resources in the background.