[GianFabien]

Motivation is an individual thing. There are no doubt at least two intersecting dimensions, i.e that of technical interest and alignment with the organization's purpose. For some people working on CRUD apps might be Ok because they are deeply aligned with the purpose.

Most people need to earn an income to support themselves. Thus you probably need to consider part-time contributors. Which in turn might require considerable project management skills to ensure that substantial units of work can be accomplished by teams of people.

Not all FOSS projects are purely by volunteers. Many contributors are actually employed to work on those projects part-time or even full-time.