I haven't seen too many cases, or possibly any case, where there wasn't an obvious pecuniary motive (to the point where I think it might be okay to limit the poison pill to commercial contexts).
If a developer or company has no pecuniary motive for proprietary relicensing, why would it bother to use copyleft for the project to begin with? Better to allow noncopyleft use by all; what is socially gained by permitting occasional discrimination (particularly where, as your comment might imply, the discrimination is always in favor of a commercial entity)?
If there were no discrimination, then any arbitrary user could get a noncopyleft license free of charge on simple request. At that point, the original decision to use a copyleft license has no rational justification.