If you peel off the layers that have accrued in some distros centralized package management is incredibly simple to implement and effective and met the performance,security, stability, and storage needs at the time of implementation. Think of it like manual transmissions. Consider the package management system of Arch or Void for instance.
As in all cases where one technology supplants another its not enough to be superior in one dimension it's a hard sell unless its not only better but substantially better for all concerns without substantial cost or downside or foisted on users from on high by someone that can't fire by switching brands.
For instance app images have been a thing for a while but nobody formalized it with a store with standards, security, testing for actual not theoretical compatibility etc so its a tool you can pick up rather than an actual ecosystem a user can rely on.
Nix/guix are cool as heck but they are also complicated and difficult to understand. They can also have issues not present in the source software
VMs are of course unwieldy
App vms are restricted to Qubes
Snap relies on a proprietary backend and starts slow among many and varied flaws.
Flatpak still starts slower than native, doesn't have most software, isn't suitable for libraries or software that will be consumed by non flatpaks, doesn't have most software.
Homebrew is mostly used by expats from Apple land because its virtues are moreso leveraging existing know how and work flows.
Docker/Podman are more like developer tooling than user tools.
Bedrock Linux is for crazy people who wish arch and ubuntu were one distro
Of these flatpak seems most likely to become the standard although I wish it would plunk an executable somewhere instead of the ridiculousness of flatpak run foo