Fair point. I'll admit to having stuck with RedHat from v6.1 to the present, apart from a very short dabble with SUSE, mainly because I much prefer yum, later replaced by dnf, to other package managers.
However, IIRC when systemd rocked up I have a feeling of the big three: Debian, RH and SUSE related distros, RH and clones were dominant and it was this, rather than anything else, that has driven systemd uptake.