The CDI system is the brains of the oufit, providing a spark and controlling ignition timing.
Stuff changes. Hence the different components over the years. Sometimes things become more advanced and/or rel;iable, sometimes a new vendor can produce the same item more cheaply, and sometimes a vendor can do both.
The verdict's still out as to which is the case on our bikes, but it's at least generally agreed that at least in terms of the CDI, gens 2 and 3 have been more reliable than was gen 1.