Because GNOME is the only DE with some potential and by not having 2 or 3 simple optional features aren’t getting more traction.
But everyone has different requirements and my “2 or 3 simple optional features” that are missing are completely different than what you think is missing. I couldn’t care less about desktop icons or system trays. I even prefer not having a system tray, as this functionality should be provided via notifications and regular application shortcuts in my opinion.
But in the end, a software project only has a limited amount of resources available and developers have to decide where they want to focus on. GNOME chose not to focus on desktop icons:
GNOME had icons, v3.28 discontinued them
Because the code was “old and unmaintained” and probably no one was willing to modernise and maintain it. Desktop icons were already disabled by default before 3.28, so they didn’t “re-invent” this feature with the removal of the code in Nautilus.
Using other DE doesn’t make much sense as you’ll inevitable run in GTK and parts of GNOME and having to mix and match to get a working desktop experience.
I use GNOME and KDE and use the same applications (as Flatpaks) on both desktops: I use GNOME Calculator on KDE, because I dislike both KDE calculators, and I use Ark on GNOME with a Nautilus script, as File Roller doesn’t allow me to set the compression ratio (I need to create zip files with 0 compression for modding games). So for me it has become the norm to mix applications created with different toolkits. Thanks to Flatpak I still have a “clean” base system though.
Btw. I am getting tired of these re-occurring complaints that GNOME works differently than other desktops. I am not constantly complaining about what features KDE is, in my opinion, missing all the time either (e. g. dynamic workspaces, same wallpaper and desktop configuration across all existing and new monitors, online account integration, command line config tool, etc.), instead I accept that this is how it is at the moment and either use KDE the way it is (like I do on my desktop PC) or use something that better suits my needs (like I do on all my laptops).
Because it takes manpower to develop and maintain these features?
Especially desktop icons are difficult to get right (see workarounds like “ReIcon” on Windows). E. g. keeping icon positions across multiple monitors and varying resolutions and displays (which can be unplugged at any time). They can also be a privacy-issue, e. g. when doing a presentation.
But most importantly: GNOME doesn’t want to be a traditional (Windows-like) desktop, so why would they implement features that don’t align with their ideas for a desktop experience?
There are lots of other desktops, like Cinnamon, that offer a traditional desktop experience within the GTK ecosystem. There is also plenty of room for desktops, like GNOME, that have a different philosophy and feature set.
In my opinion it would be boring, if every desktop tried to do the same thing. And there wouldn’t be any innovation, if no one tried to do things differently.
I’ve tried to combat this a bit with a global Flatpak override that takes unnecessarily broad permissions away by default, like filesystem=home, but apps could easily circumvent it by requesting permissions for specific subdirectories. This cat-and-mouse game could be fixed by allowing a recursive override, such as nofilesystem=home/*.
But even then, there is still the issue with D-Bus access, which is even more difficult to control …
I think it is sad that Flatpak finally provides the tool to restrict desktop apps in the same way that mobile apps have been restricted for a decade, but the implementation chooses to be insecure by default and only provides limited options to make it secure by default.
I am surprised that no one has mentioned Rnote yet.
It is my favourite newly-created program for Linux. It is a relatively new app which supports annotating files and taking handwritten notes. You can import PDFs, set the page size to infinite or a fixed size (something OneNote can’t do), adjust the background to display grids or lines or dots or nothing with any spacing you like, input text with your keyboard, … It is available on Flathub for easy installation.
The only major downside is the following: Disclaimer: The file format is still unstable. It might change and break compatibility between versions.
You don’t need your own server to use Joplin. You can select a local directory to store your notes and sync this directory with Syncthing between devices.