Fedora Silverblue is in an entirely different ball game. You can’t use dnf because it’s an immutable image based system where you can’t make direct changes to the Root system without making use of the rpm-ostree & VCS mechanisms. You’re making a conscious choice by using Fedora Silverblue, and the pros out way the cons for most people making that choice.
In contrast Fedora Workstation allows you to use dnf just as normal because it’s not an immutable image based system.
Ubuntu doesn’t make use of any such system so their reliance on containerized user-space apps isn’t a technical one.