That's a completely different product than Fitbit is. Even its full blown smartwatches are very light, very dumb peripherals with very low power that last a week on a charge. They're really not the same type of product as a Wear OS or Apple Watch type device, and trying to turn them into one will take away all of why Fitbit owners choose them.
Well there's also market segmentation you know. Xiaomi is entering the Wear OS smartphone market, no reason why FitBit couldn't also. This move from Google is obviously a way for them to speed up their own watch tech so that they don't have to start from scratch. This doesn't mean there wont be these simpler dumber versions of smartwatches for the people who want exactly those
