I agree in principle, but it's worth pointing out that Snap is designed for end-user applications, so it's unlikely to be used on a server or in a Docker image built for deployment.
Plus I want my workstation to be as similar as possible to the deployment container to make debugging easier. So if I feel uncomfortable using Ubuntu 20 for my workstation, I should probably switch my deployment docker base image, too.
They started building it for IoT, whereas Flatpaks were designed for the desktop from beginning.