Networkd is a pain to configure and operate, and interferes with the lower level subsystems. Resolved is a mess that only causes headaches. It might be ok-ish on desktops but honestly I never had an issue with regular /etc/resolv.conf on any of my laptops and desktops. Journald is a (terrible) solution looking for a problem and makes everything more opaque and harder to troubleshoot.

Containerisation and namespacing is a big mess and lacking on basic features. It also doesn't play nice with the core tooling (ip netns, etc).

I like the service units but honestly we could all have done without it. There were already other perfectly usable solutions in that space. I used runit for a while before nearly every distro out there caved to systemd.