I have been viewing an American patent that was originally issued in Germany, and it shows "Complete Disclaimer" under "Legal Events":

LEGAL EVENTS
Date Code Event Description
Mar 25, 2010 8330 Complete disclaimer
Jan 11, 2001 8364 No opposition during term of opposition
Jul 13, 2000 D2 Grant after examination
May 7, 1998 OP8 Request for examination as to paragraph 44 patent law

I gather that means the licensee was essentially waived rights under the patent (?) by saying that his claims under the patent are abandoned.

Is that correct? Why would anyone do that, rather than just neglecting to pay a fee?