* GSoC has had a tendency to rotate open source projects. Lots of new projects seem to have been added, and some others will have to go. * In general this year there seem to be a lot of science (bioinformatics, geospatial, etc) projects, more than before, and that may be due to a changing focus. * The Mozilla foundation is not a small organisation and could afford for internships themselves, in fact I believe they did just that in the last few years.
[1] https://twitter.com/tonroosendaal/status/572473379648888832
[1] https://blog.mozilla.org/blog/2014/11/19/promoting-choice-an...
I don't think it would be for rivalry, it maybe just that they wanted focus more on getting more contributors to the new organisations that really need exposure and contributors. Also if it was rivalry would easily do it elsewhere and probably not at GSoC.
btw, http://planet.mozilla.org give a read
"over 130 projects were dropped and over 80 new projects added"