Except desktop environments - they are far from a simple loosely collection of simple stuff. They coordinate your whole desktop experience. Apps need to talk to them a lot and often in ways specific to a single DE. Theming applications is done differently for every toolkit there is, startup applications (before systemd) is configured differently, global shortcuts are configured differently by each one... If anything it is something you interact with far more than systemd and has far more inconsistencies between each one. Yet few people complain about this as much as they complain about systemd.

Systemd is a giant mess of weirdly interdependent things that used to be simple things.

They used to be simple things back when hardware and the way we use computers were much simpler. Nowadays hardware and computers are much more dynamic and hotplugable and handle a lot more state that needs to persist and be kept track of. https://www.youtube.com/watch?v=o_AIw9bGogo is a great talk on the subject and talks about why systemd does what it does.

What standards? The old init systems were a loose collection of shell scripts that were wildly different on every distro. Other tools like sudo also broke the established standards of the time, before it you had to login as root with the root password.

Even gnome and KDE have their own themeing standards as well as other ways of doing things. Even network manager is its own standard not following things that came before it. Then there are flatpack, snaps and app images. Not to mention deb vs rpm vs pacman vs nix package formats. Loads of things in Linux userland have broken or evolved the standards of oldern times.