I honestly don't understand the point you are making except to be contrarian.
There's nothing contrarian about it. It's the reality that these systems have followed. You're saying that they should all change how they current operate, or should've done so in the past. I'm explaining why they operate the way they do. My view reflects what is currently happening, and thus the mainstream, not the alternative.
You're trying to argue nuh-uh don't need them,
I never did such a thing. I simply explained why they aren't universally adopted and that by the fact that they essentially bundle half an operating system inside, people don't like them as much. There's a good reason this approach hasn't won out: it means a far bigger resource drain on the system and that that the specific philosophy of the operating system, the very reason people chose that operating system to begin with, is not being respected.
They exist in Steam because game devs don't want to build, test and maintain the same game for multiple dists. They exist in applications because imposing a time and effort penalty on devs to build, bundle, package and test their app for every dist is stupid.
And how successful is all that compared to instead installing software the standard way from the distributions repositories? This approach isn't really winning in the end and people like the traditional way better because it turns out they don't want to pay twice the resource amount and they want software to actually work the way they want it to, rather than how the developer wants it to.
And that's not even mentioning other benefits like sandboxing,
Containers have nothing to do with sandboxing and it's a pervasive myth that they function as one. They need a sandbox on top of it, which can also be used without a container. Running untrusted software inside of a container does not mean it can't escape.
generating sboms and receiving more timely app updates from the app maintainers without waiting for updates to filter downstream.
People run Debian exactly because they don't want timely updates. This is where I feel you simply don't understand the differing philosophies of different operating systems. Debian is specifically chosen for it's stability, by which they don't mean “doesn't crash” but that they guarantee that the system won't change outside of major version changes or fixes required to fix critical bugs only. Non-critical bugs are not fixed, they are documented, this is by design. It is very attractive to many uses that the system remain unchanging. These people do not want to wake up at one point and realize some interface changed or something doesn't work any more the way it used to and want to concentrate that on major version updates and they want these versions to have long-term support so that they need to update as infrequently as possible.
This is why they choose Debian; this is one of it's main sells. This is why Debian doesn't update to new versions to fix critical bugs but backports the fix to old versions and this is exactly why bundling half an operating system inside of a container that may not respect the Debian philosophy isn't attractive to Debian users. They choose Debian for a reason, and that reason is typically that the system is unchanging and software doesn't update.
And half an OS? Nope. Most containers formats allow apps to define a dependency on a runtime or a base image and then they only contribute their difference compared to the base image, i.e. their own files. If multiple apps share the same runtime, the runtime is shared.
If you have the required o.s. outside of it in the right version perhaps, but otherwise all sorts of things such as Pulseaudio of Pipewire, and all that are included inside of the Flatpak container. Not to mention that it requires things such as Dbus to work to begin with, which I personally don't have installed.
And glibc? That depends on the use case. Alpine Linux (a whopping 5mb overhead) uses musl libc for example and plenty of images exist on top of it.
Yes but Steam doesn't, which is what this was about. As far as I know it hard depends on glibc.
But feel free to not use them. If you're a masochist, do it the Gentoo way and build everything from source.
And here we go. The standard Freedesktop “my way or the highway” complete lack of perspective on the needs and desires of others. Everyone who can't see the great Freedesktop designs is a “masochist” or something similar and that's always the thing that's holding back adoption of the latest Freedesktopware. Wayland still not seeing close as much adoption as X11? That's always of course because people are “masochist” and can't see the greatness and how much better it is. It has nothing to do with that they simply like different things and have different needs.
There are obviously reasons people use Gentoo such as extra performance, customization of compilation options and ease of applying custom patches as well as picking the exact version of whatever package one wants and freely mixing that with other versions of other packages. This all falls apart when using Flatpack which is why Gentoo users seldom use it. I actually just yet tried to install flatpack for fun on a Gentoo system. It didn't do it because it wanted dconf which is masked on my system because I certainly don't have the time to figure out how a binary configuration store works when I could just be editing plain text files that are human readable. Of course, in all it's glory and splendor, the Freedesktop sages will tell you that you should never store configuration in plain text files, despite it being the most common way around because their way is the highway.
Whoops, you've just installed Flatpak! And so does Debian. Funnily enough Debian also maintains docker images, e.g. bookworm-slim. Maybe you should email the maintainers and explain how this is all against their philosophy.
People can install whatever they want. But in the end of the day they aren't popular with the users for the reasons I outlined above. People will much rather install a package with apt-get than with Flatpack because then they get the version of it that does conform to the Debian philosophy.