The main reason, I'd say (at least by the time of the Cygnus acquisition) the only reason, for copyright assignment for Cygwin was to ensure that Cygnus/Red Hat

The main reason, I'd say (at least by the time of the Cygnus acquisition) the only reason, for copyright assignment for Cygwin was to ensure that Cygnus/Red Hat was the sole GPL licensor. Thus Cygnus/Red Hat, and only Cygnus/Red Hat, could offer alternative for-fee license arrangements. This was the basis of the business model. Copyright assignment isn't the only means of achieving that result with a GPL-licensed project, but it was the traditional technique and probably the soundest from a legal perspective. Red Hat is phasing out this commercial model for Cygwin. Hence single-licensor GPL licensing is no longer necessary or, I'd say, appropriate. It has nothing directly to do with litigation issues in any general sense. By 2020, I expect that all contributions to Cygwin will be made under the LGPL, meaning that there will potentially be a diversity of LGPL licensors in contrast to the situation prior to today where there was one GPL licensor.