I'd also add that systemd appeals to application developers (no daemon code, one file for all distros). And it appeals to sysadmins too (no more /etc conflicts on any package update! Modify any system service! etc..)

Which brings me to the question of which category systemd does not appeal to? I am guessing "minimalists" and "people who like things done the old way" - and those are simply not that numerous compared to others.