The BSDs have far less lock-in with the default components than Linux distributions usually do. For example, I dislike the default syslog daemon, so, I disabled the default, and used my own. This involved adding two lines to /etc/rc.conf --

    syslog_ng_enable="YES"
    syslogd_enable="NO"

and that was it. Unlike systemd's way of doing it, the default syslog facility isn't started at all, doesn't run, period. Pretty much all the other low level services -- crond, dhcpd, ntpd, etc -- are the same way. This is one of the many failings as to how systemd operates. One should have reasonable defaults, but at the same time, if the defaults don't work, it should be easy to change them.

I think people don't like systemd because it (in their view) has major flaws, and the lock-in prevents other systems from being tried.