every contributor has independently licensed the portion of the code they contributed under the current license. so most larger FOSS projects require a Contributor License Assignment to the org managing that project such that changes like these are legally feasible. otherwise you have to track down every person who made a one line change or risk getting sued for copyright infringement.

when you work for a corporation this license assignment is a standard part of the employment contract for this exact reason. our copyright system is deeply broken.