In a "I never actually had to write any code which had significant interaction with existing solutions (openrc, upstart, sysv, bsd, whatever), but I know they exist, so I'll talk about them like they solve the same problems as systemd" way. Which they do not. Want socket activation, double forking, namespaced children, sane scripts/unit files that can build a good dependency tree? You have one option.
Additionally, people see other tools like systemd-network and say "but systemd is doing everything!" Which it isn't. Almost no distros package those as part of the default.
Even if they did, many of the anti-systemd crowd would rather live with a different, slower system (NetworkManager, for example) which is vastly most complicated than what they need. Ditto for systemd-resolved and local caching dnsmasq.
Systemd is not trying to replace NM or BIND or anything. It's basically saying "it's 2019. If you want to be able to work with a system without knowing the ins and outs of 30 different configuration files, and speed up boot time/auditability of your system significantly, you can use these services"
Some things are bad for the community in general. The dependence on dbus (and kdbus), systemd-logind, and other tools aren't very friendly to BSDs to anti-systemd distros. Frankly, from my POV, this isn't systemd's problem. The anti-distros are free to do what they want, knowing the limitations. The BSD guys have written compatibility layers, which you can do, because they're open standards.
Broadly, I'd say that the anti-systemd crowd holds to an idea of "UNIX" purity, as if HP-UX, Tru64, AIX, Solaris, IRIX, and others were uniform. The reality is that they were more different than they were alike, in terms of administrative tools, filesystem layout (is this /sbin/init.d, /etc/rc.d, /sbin/rc.d, etc?) and even software portability. A large reason that GNU autoconf exists is to detect all of the quirks on all of these platforms.
Additionally, anti-systemd people either never used X11R6/OSS/lilo and other old tools, or don't remember how terrible they were. Any large change in the community (X.org fork, ALSA->PulseAudio, grub) draws ire. From the same people who are trying to use syslinux and efibootmgr instead of just using grub2.
Some people would rather debate philosophy than get actual work done, and that's great for open source, even if it's frustrating. But those people never dug into the guts of upstart to make something work, or had 250 lines of sysvinit boilerplate+supervisord saved off somewhere to speed up a process that you can do in 4 lines in a systemd unit file.