Prior to systemd, the lack of a standard init/rc/service monitoring system meant that you could pick and choose 3 different solutions for those 3 problems. systemd is pushing for unifying not just those 3, but other systems too (gummiboot, consolekit, udev). As more software becomes designed to work just with the systemd ecosystem, more people who have love for one of the systems that has been subsumed will feel forced to switch.
Say you have a favorite fork. You eat lunch with it everyday. Now at your favorite restaurant for takeout, the manager says "We switched salad dressings, and the new dressing line isn't compatible with that fork, you'll need to use this one instead." The fork that the manager hands you may be perfectly fine (better in some ways, worse in others than your favorite fork), but it's not your fork. So you sadly stop going to that restaurant. But then you notice something: more and more restaurants are switching salad dressing suppliers, so now you have to either give up your favorite fork, or use only salads you make yourself. You're probably going to be mad at the salad dressing company.