Well, it’s not that simple. Ubuntu, for example, doesn’t correspond to any single Debian version, since they pull from Debian sid
, freeze at some point, and then skin it with their own theme and such. And at some point, they had tried to develop an alternative init system (upstart
), alternative display server (mir
), and alternative desktop shell (unity
). All were ultimately failures, and it sort of soured the Linux community at-large on Ubuntu and Canonical.
Then take Linux Mint, which has both an Ubuntu-based version and Debian-based version, both of which get combined with their own software and defaults (disabling snap
, enabling flatpak
, driver locator/defaults, etc).
Or take some that are based on none of the above, like Void or NixOS or GUIX or whatever. Or take some more mobile-focused distros like Alpine or postmarketOS.
My point is that yes, maybe there are “too many” distros. But from what I know, most of the distro-specific work gets upstreamed when possible (e.g. Canonical has a bad reputation because they’re perceived as not really contributing to upstream, implying most distro developers do contribute to upstream projects). And while there is a decent amount of fragmentation, I’d argue it’s not really on the distro level per-se, but rather at the graphical toolkit (GTK+{2,3,4}, Qt{4,5,6}, wxWidgets, etc) and desktop environment/window manager/compositor (Gnome, KDE, Xfce, LXDE, AwesomeWM, Sway, i3, *Box, etc) levels.
There are lots of different distros because there are lots of different opinions around which release cadence and level of stability is right, how often new software should be introduced into one release, and so on. And I understand that might be intimidating for a potential new user, but I don’t really see any way of solving that and most new users get redirected to Ubuntu, Linux Mint, and sometimes Fedora. So it’s not like new users are given the full breadth of choices and that’s okay (they’ll be waiting when the user is ready).
In the same vein, I understand why there are different desktop environments and window managers/compositors. There are drastically different design choices surrounding how they’re configured, what options are provided, and whether they’re scriptable and heavily extensible. And again, in this area, the choice isn’t really a problem because new users are generally directed either to Gnome or KDE.
The toolkit case, however, is a bit more annoying. This diversity leads to inconsistencies in HiDPI support (GTK+2 is terrible at this, whereas GTK+3 and above are better), theming inconsistencies (Gtk and Qt use different themes and getting them to play nice is a hassle), and mostly feels…stupid. I really wish we only had one graphical toolkit because it would fix some of the papercut issues that keep cropping up.
All of that being said, my point is simply that most of the diversity in distros doesn’t really affect anything because new users tend to enter through a handful of distros and the rest are there waiting for when they’re ready (if they want to explore at all).