I don't think the phrasing is correct. Your choice of word (spread/ingrain itself) seems to imply there is malicious intent. Software do not sneak itself into distribution by themselves. It is the other way around. Distribution creators have total freedom on what components/software they find useful to build their distributions on. If a majority of distros decided to use systemd, that mean a majority of people maintaining distributions found the positive outcomes of using systemd were worth dealing with any disadvantage it may had over using another solution.