Starting to charge is difficult

When an existing Open Source project is managed and developed by volunteers primarily, all of the currently involved "members" who are familiar with the inside working are probably already employed somewhere and get their paycheck for doing something (else).

There is then a challenge in then trying to take on paid projects to further develop the project as the best skilled developers have full-time jobs that keep them busy on other things and which also in many cases forbid them to take on contracting jobs on the side as many employees have that mentioned in their agreements or contracts with their employers.