systemd became a standard because the guy works at Red Hat so he can make GNOME require it (there is no way to use GNOME without systemd; distros that allow that such as Gentoo do so by patching GNOME, which is costly.)
I agree that a more modern init system is necessary, but the idea of systemd is meh and the implementation is subpar.
You make it sound like the systemd author was something the CEO of all Linux Distros.
The maintainers of Arch Linux have given an explicit list[1] of the reasons why they decided to introduce systemd:
0) it is hotplug capable
1) we can know the state of the system
2) it is modular
3) it allows dbus/udev to go back to doing the task they are meant to do
4) we can reduce the number of explicit ordering dependencies between daemons
5) we get a lot of security/sandboxing features for free
6) systemd service files can be written and distributed upstream
7) systemd is a cross-distro project
8) logind will finally deliver on what consolekit was supposed to do
9) systemd is fast
systemd became a standard because Debian adopted it after a lengthy discussion, partially because big Debian users like Spotify expressed an interest in systemd.
The intentional and willful breaking of screen and tmux was to fix a GNOME bug of GNOME not closing up as it should when the user logs out, so systemd was changed to mass kill processes. The interplay between GNOME and systemd in backroom dealings is a major pain point.
I think that's an oversimplification. There are definitely cases where some thing started as a daemon under a user session, graphical or not, should be killed to be safe. For example, ssh-agent.
There are other things that are meant to be left around, as that's their purpose, such as screen and tmux.
I would say the safe solution would be to kill everything in the user session at multiple levels (GNOME, and user session management demon like logind, etc), and to provide a defined safe way for the very few programs that want to stick around to do so. That seems like what systemd came up with as well.
I don't believe this to be a "conspiracy". It's nothing shadowy, really. What they did is completely natural. That doesn't mean I support the idea though.
I agree that a more modern init system is necessary, but the idea of systemd is meh and the implementation is subpar.