Why switch to systemd when the concept of init and run levels seemed to work for 40 years! If it isn't broke, why try to fix it?

Yes, the concept is very easy to understand. On the other hand, with modern operating systems, there is pressure to "evolve" into more efficent running operating systems. For example, in many ways both Apple creators and Unix/Linux creators have influenced each other to build better operating systems over the past decade. The Apple Mac OSX operating system uses a variation of the Unix kernel. On the other hand, Unix/Linux developpers have noticed Apple's method of running services in parallel as opposed to in sequence.

Here is an example comparing init vs systemd:

(Reference: [http://www.youtube.com/watch?v=TyMLi8QF6sw (beyond init: systemd)] )

The init process may force certain services to be launched in a particular sequence. For example, the Bluetooth process cannot launch until the avahi process launches. On the other hand, the avahi process cannot launch until the D-BUS process launches, which cannot start until the syslog process is launched.